bitbake: bitbake-user-manual-metadata.xml: Added second conditional metadata example.

bitbake: bitbake-user-manual-metadata.xml: Added second conditional metadata example.

I think having a couple real-life examples here would make a huge
difference.

Comment from Scott: I modified the example description to indicate
that it is from an OpenEmbedded metadata-based recipe (i.e from
YP).  We have been trying very hard to keep the BitBake User
Manual as separate as possible from the YP docs.

(Bitbake rev: 834780772a08ecce7ed863e96d0674b47d0e589d)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>