board-status.html: improve instructions

The foreword mentioned that you need a gerrit account, but not how to
have git push with the right credentials.
To ease onboarding, point out where to get them.

Change-Id: I0b022bc064e3bc89568617c1a3a3e0e5236ba520
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/29240
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/docker/coreboot.org-status/board-status.html/foreword.html

@@ -18,7 +18,11 @@ devices are well-tested.  We have
 <a href='https://review.coreboot.org/cgit/coreboot.git/tree/util/board_status'>a tool in the coreboot repository</a>
 to make contributing easy.  The data resides in the
 <a href='https://review.coreboot.org/gitweb/cgit/board-status.git'>board status repository</a>.
-Contributing requires an account on review.coreboot.org</p>
+Contributing requires an account on review.coreboot.org. After
+logging into the site with your preferred OpenID or GitHub/Google
+credentials, you can get a user name and password for git pushes on <a
+href="https://review.coreboot.org/settings/#HTTPCredentials">gerrit's
+settings screen</a>.</p>
 
 <p>Sometimes the same board is sold under different names, we've tried to
 list all known names but some names might be missing.</p>