bitbake: user-manual: Added "Hello World" Appendix.

bitbake: user-manual: Added "Hello World" Appendix.

I took Bill's chapter and made it into an appendix.  I did some
re-writing to make it not so much like a getting-started feel,
although it still leans way that way for an appendix.  The content
is not complete.

Had to add in a line to the user-manual.xml file so that the
new appendix would be part of the book.

Had to use a different form of the command in the
user-manual-cusomization.xsl file in order to not through a bunch
of errors for an unrecognized parameter value.  I commented out
the existing one.

(Bitbake rev: 80e9306c288ca2ab42585f99fb0f396253cb8253)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>