Instructions create a github account in workshop preparation.

This should enable participants who don't yet have a github account
in their own time, so they're less likely to end up with "yet another
account at some website".

index.html

@@ -465,6 +465,15 @@ <h3>Git</h3>
     web browser (current versions of Chrome, Firefox or Safari,
     or Internet Explorer version 9 or above).
   </p>
+  <p>
+    You will need an account at <a href="https://github.com/">github.com</a>
+    for parts of the git lesson. Basic Github accounts are free. We encourage
+    you to create a Github account if you don't have one already.
+    Please consider what personal information you'd like to reveal. For
+    example, you may want to review these
+    <a href="https://help.github.com/articles/keeping-your-email-address-private/">instructions
+    for keeping your email address private</a> provided at Github.
+  </p>
 
   <div class="row">
     <div class="col-md-4">