add stack overflow to help page

app/views/help/index.html.haml

@@ -27,6 +27,8 @@
         %li
           Ask in our
           = link_to "support forum", "https://groups.google.com/forum/#!forum/gitlabhq"
+          or on
+          = link_to "Stack Overflow", "http://stackoverflow.com/questions/tagged/gitlab"
         %li
           Browse our
           = link_to "issue tracker", "https://github.com/gitlabhq/gitlabhq/issues"