documentation/kernel-manual/kernel-how-to.xml: fix to step 3 and 4 of section 3.4.4
Added text after the sample bbappend file stating that the user needs
to update the KSRC assignment statement and also remove its comment.
Also they have to remove the comment from the SRC_URI line.
Changed the bitbake command in step 4 to use the linux-yocto-stable
file rather than the linux-yocto file.
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
