dev-manual: Added note about RPM not dealing with post-install

dev-manual: Added note about RPM not dealing with post-install

Fixes [YOCTO #10351]

I added a note to the "Post Installation Scripts" section of the
"Writing a New Recipe" section to call out the fact that the
RPM package manager will not install packages on the target when
any RPM post-install script returns a non-zero exit code when
the script is run on the target.

(From yocto-docs rev: a2b36b4a352522e3c576a45ee239af51eda518c1)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>