doc/contribute.html rewrite "Set up auth... code review".
- Fixed term in preceding section: submitted -> merged.
- Clear transitions between web sites.
- Clarify "types" of G Accounts.
- Less verbose "Configure Git" instructions. [l10n]
- Google uses the term "sign in".
- Mention .gitcookie file created.
Update "Register with Gerrit".
- Link directly to gerrit /login/ .
HTML
- Removed non-ascii "hidden characters".
- Encoded some & and >.
Change-Id: I0d99102def6b32e09b8e42fa40e20227ad5e7568
Reviewed-on: https://go-review.googlesource.com/5892 Reviewed-by: Andrew Gerrand <adg@golang.org>