Handle tricky problems to get subtitles working on intro video

First and foremost, the mime type has to be supported by the web
server.  Either you have to add a `.vtt` mimetype, *or* just put it
as a `.txt` file.  I chose the latter since it doesn't require a
custom Apache configuration.

Second, even if you make it a `.txt` file, using a CDN does not seem
to work.  I suspect that maybe CDNs do really weird things with
mimetypes when they server them, or maybe the <track> element just
really doesn't like it when the URL is 301'd. 🤷

Anyway, with these two changes: using a `.txt` file, and hosting the
file locally, the subtitles now work properly!

Note, if you use the `default` attribute in the <track> tag, it'll
turn them on by default.  Leaving it off does allow the user to turn
them on in my tests in both Chromium and Firefox.

www/conservancy/static/docs/sfc-introduction-vtt-captions.txt

@@ -0,0 +1,161 @@
+WEBVTT
+
+1
+0:00:10.880 --> 0:00:15.920
+<v Karen Sandler>Software Freedom Conservancy is a non-profit 
+organization centered around ethical technology
+
+2
+0:00:16.800 --> 0:00:22.560
+<v Karen Sandler>our mission is to ensure the right to repair 
+improve and reinstall software we promote and
+
+3
+0:00:22.560 --> 0:00:26.560
+<v Karen Sandler>defend these rights through fostering 
+free and open source software projects
+
+4
+0:00:26.560 --> 0:00:31.600
+<v Karen Sandler>driving initiatives that actively make technology 
+more inclusive and advancing policy strategies
+
+5
+0:00:31.600 --> 0:00:36.720
+<v Karen Sandler>that defend software freedom to forward these 
+goals Software Freedom Conservancy takes a three
+
+6
+0:00:36.720 --> 0:00:42.000
+<v Karen Sandler>branched approach copyleft advocacy diversity 
+and inclusion and supporting alternatives
+
+7
+0:00:42.640 --> 0:00:47.840
+<v Karen Sandler>free and open source software or FOSS for short 
+is software that protects your rights and freedoms
+
+8
+0:00:47.840 --> 0:00:51.360
+<v Karen Sandler>developers work hard to write FOSS and 
+Software Freedom Conservancy is here
+
+9
+0:00:51.360 --> 0:00:56.400
+<v Karen Sandler>to protect and preserve your freedoms 
+ensuring the right to view modify share
+
+10
+0:00:56.400 --> 0:01:02.080
+<v Karen Sandler>and use the software for any purpose free 
+software like copylefted software ensures
+
+11
+0:01:02.080 --> 0:01:05.600
+<v Karen Sandler>that software stays free in the future 
+as more and more people contribute to it
+
+12
+0:01:06.720 --> 0:01:10.960
+<v Karen Sandler>copyleft is a kind of software licensing 
+that leverages the restrictions of copyright
+
+13
+0:01:10.960 --> 0:01:16.400
+<v Karen Sandler>but with the intent to promote sharing this helps 
+consumers make sure their devices can be updated
+
+14
+0:01:16.400 --> 0:01:22.720
+<v Karen Sandler>and last longer avoiding premature obsolescence 
+Software Freedom Conservancy defends your rights
+
+15
+0:01:22.720 --> 0:01:27.200
+<v Karen Sandler>as a consumer from companies who seek to deny 
+these rights despite their responsibilities
+
+16
+0:01:28.400 --> 0:01:32.400
+<v Karen Sandler>Software Freedom Conservancy helps hold 
+companies accountable for the software that
+
+17
+0:01:32.400 --> 0:01:39.840
+<v Karen Sandler>is included in millions of devices worldwide 
+and upon which millions of consumers rely
+
+18
+0:01:40.480 --> 0:01:44.960
+<v Karen Sandler>free software is truly borderless and at 
+Software Freedom Conservancy we strongly
+
+19
+0:01:44.960 --> 0:01:49.440
+<v Karen Sandler>believe that no one should be denied access to 
+valuable information creating a level playing
+
+20
+0:01:49.440 --> 0:01:53.680
+<v Karen Sandler>field for everyone in our free software 
+community conservancy helps by bringing to
+
+21
+0:01:53.680 --> 0:01:57.920
+<v Karen Sandler>light and providing support for historically 
+excluded communities and technology spaces
+
+22
+0:01:58.480 --> 0:02:03.200
+<v Karen Sandler>in particular those subject to systemic bias 
+and who are impacted by underrepresentation
+
+23
+0:02:06.960 --> 0:02:11.760
+<v Karen Sandler>in today's high-tech world reliable software is of 
+the utmost importance for our daily work and play
+
+24
+0:02:13.120 --> 0:02:17.840
+<v Karen Sandler>this is why Software Freedom Conservancy is proud 
+to support industry-grade software applications
+
+25
+0:02:17.840 --> 0:02:22.640
+<v Karen Sandler>that help everyone all over the world work 
+and play better faster and with more freedom
+
+26
+0:02:23.200 --> 0:02:27.200
+<v Karen Sandler>FOSS applications allow you to retain 
+complete control over everything you make
+
+27
+0:02:27.200 --> 0:02:32.320
+<v Karen Sandler>and they work cross-platform this not only 
+makes for more cooperative working environments
+
+28
+0:02:32.320 --> 0:02:36.320
+<v Karen Sandler>but breaks down barriers imposed 
+by proprietary software vendors
+
+29
+0:02:36.320 --> 0:02:42.400
+<v Karen Sandler>ensuring everyone can work freely without giving 
+away their privacy autonomy or user rights
+
+30
+0:02:43.840 --> 0:02:49.920
+<v Karen Sandler>free software is your software here at software 
+freedom conservancy we work towards a future where
+
+31
+0:02:49.920 --> 0:02:56.880
+<v Karen Sandler>user freedoms are the highest priority come join 
+our pursuit for a better digital world this cannot
+
+32
+0:02:56.880 --> 0:03:03.840
+<v Karen Sandler>happen without you please take a moment and become 
+a Software Freedom Conservancy sustainer now

www/conservancy/templates/frontpage.html

@@ -48,7 +48,7 @@ strategies that defend FOSS (such as copyleft). <a href="/about" class="orange">
 <section class="mh0 pa3 bg-light-blue ba b--gray">
 <p><video style="width: 95%; height: auto;" controls="" poster="/videos/sfc-introduction-video_poster.jpg">
 <source src="/videos/sfc-introduction_1080p.mp4" />
-<track src="/videos/sfc-introduction.vtt" kind="subtitles" srclang="en" label="English" />
+<track src="/docs/sfc-introduction-vtt-captions.txt" kind="subtitles" srclang="en" label="English" />
 <a href="/videos/sfc-introduction_1080p.mp4"><img src="/videos/sfc-introduction-video_poster.jpg" alt="Software Freedom Conservancy introduction video"></a><br/>
 <a href="https://youtu.be/yCCxMfW0LTM">(watch on Youtube)</a>
 </video></p>

www/conservancy/templates/supporter/index.html

@@ -54,7 +54,7 @@
 <p style="text-align:center;">
 <video style="width: 50%; height: auto;" controls="" poster="/videos/sfc-introduction-video_poster.jpg">
 <source src="/videos/sfc-introduction_1080p.mp4" />
-<track src="/videos/sfc-introduction.vtt" kind="subtitles" srclang="en" label="English" />
+<track src="/docs/sfc-introduction-vtt-captions.txt" kind="subtitles" srclang="en" label="English" />
 <a href="/videos/sfc-introduction_1080p.mp4"><img src="/videos/sfc-introduction-video_poster.jpg"
                                                   alt="Software Freedom Conservancy introduction video"></a><br/>
 <a href="https://youtu.be/yCCxMfW0LTM">(watch on Youtube)</a>