Fix the formatting of the note on the Vulkan-Headers auto-roll failing.
Also add information about performing a manual roll when multiple
dependent repos have to be rolled in unison.

Bug: angleproject:1944
Change-Id: I0acee1531f46e8dec67666de5eb18715dc012fe9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2148493Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tobin Ehlis <tobine@google.com>