Add items to "quick help"

Modify the quick help list to add links to the pricing and feature
comparison pages of about.gitlab.com.

app/views/help/index.html.haml

@@ -42,3 +42,9 @@
         %li
           Use
           = link_to 'shortcuts', '#', onclick: 'Shortcuts.showHelp(event)'
+        %li
+          Get a
+          = link_to 'support subscription', 'https://about.gitlab.com/pricing/'
+        %li
+          = link_to 'Compare', 'https://about.gitlab.com/features/#compare'
+          GitLab editions