I walked through the steps for a contribution but ended up
with an error when doing "git mail" because I didn't have a
signed agreement.

Added a section to check for or create one through Gerrit right
after the user has created the account and logged in.

Moved some info from copyright section to the new section.

Change-Id: I79bbd3e18fc3a742fa59a242085da14be9e19ba0
Reviewed-on: https://go-review.googlesource.com/13062Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>