kernel-dev, mega-manual: kernel dev flow fig update and chapter revs

Updated the kernel development flow diagram to have an arrow from
the repositories to the box that says you need to clone the
kernel repository.  Also, provided some wording changes in the
end of the chapter.

(From yocto-docs rev: c77cff4f7b0795d5429dc47c2ad63aec6d19d513)

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

documentation/kernel-dev/kernel-dev-intro.xml

@@ -250,6 +250,9 @@
                 on actual hardware or perhaps QEMU.
                 </para></listitem>
         </orderedlist>
+        The remainder of this developer's guide covers common tasks typically
+        used during kernel development, advanced Metadata usage, and Yocto Linux
+        kernel maintenance concepts.
     </para>
 </section>