[BUGID# 873] - documentation/poky-ref-manual: Notes added for non-GPLv3 builds

[BUGID# 873] - documentation/poky-ref-manual: Notes added for non-GPLv3 builds

[BUGID# 873] - Added a note in the Images Appendix indicating that
building an image without GPLv3 components is only supported for
base and minimal images.  Also put the two changes you have to do
to the local.conf file for the build.

Added a note in the second chapter in the section on building images.
The note indicates the same as in the appendix but does not go into the
local.conf file detail.

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>