manual: update review process and patchwork

manual: update review process and patchwork

Adding more documentaiton based on discussion from the mailing list
in regards the buildroot review process and how patchworks can be
used to pull in patches for testing purposes.

Mailing list discussion:
http://lists.busybox.net/pipermail/buildroot/2013-September/078170.html

Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>