1. Updates tools/build-all-rst.sh so that it does not get published
to /draft.
2. Updates www/templates/contributor_guides.tmpl with the link and name
of the new guide.
3. Updates the How to Contribute link on the index.html pages.
Change-Id: If2331b393e1998d5f561cf4c2662c76cf507ced0
Implements: blueprint docs-contributor-guide
e16c6d9493