Some discussion about this variable indicated that the importance
of the immediate expansion operator was not being called out
enough. I added further information to the existing note that
states to be sure to use ":=" when using the variable.
(From yocto-docs rev: b97d3fa714a7c71356cd00548d3d01280034afc2)
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>