Update invite email to make it clear a button needs to be pressed

pinaxcon/templates/symposion/emails/teams_user_invited/message.html

@@ -6,7 +6,7 @@
     </p>
 
     <p>
-        To accept this invitation, visit the following url:
-        <a href="http://{{ site_url }}{{ team_url }}">http://{{ site_url }}{{ team_url }}</a>
+        To accept this invitation, visit 
+        <a href="http://{{ site_url }}{{ team_url }}">http://{{ site_url }}{{ team_url }}</a> and click the "Join" button.
     </p>
 {% endblocktrans %}