Add a paragraph to the top of the section on buildhistory mentioning the
metadata-revs file and the top-level directories.
(From yocto-docs rev: ae7c7c64dd31f5b5c57eac9c772972523f49c05a)
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>