Fixes [YOCTO #9988]
Updated the STAGING_DIR_TARGET variable with a better introductory
sentence.
Updated the MULTIMACH_TARGET_SYS variable with a more expanded
explanation.
Added a new glossary entry for the MULTIMACH_HOST_SYS variable.
(From yocto-docs rev: d17873d695772b62325de35dd0e5b9ccc7f12f1a)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>