ref-manual: New section on patching for expanded build process

Fixes [YOCTO #2808]

Added a new sub-section to the BitBake section that takes a
closer look at the build process.  Part of the requirements
was a new figure that had to be added to both the ref-manual
and the mega-manual figures directories.

(From yocto-docs rev: c40476b079cf5765b8228502f0ef33072f8b2b85)

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

documentation/ref-manual/technical-details.xml

@@ -1031,6 +1031,41 @@
                 building goes on for a given recipe.
             </para>
         </section>
+
+        <section id='patching-dev-environment'>
+            <title>Patching</title>
+
+            <para>
+                Once source code is fetched and unpacked, BitBake locates
+                patch files and applies them to the source files:
+                <imagedata fileref="figures/patching.png" align="center" width="6in" depth="5in" />
+            </para>
+
+            <para>
+                The <filename>do_patch</filename> task processes recipes by
+                using the
+                <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
+                variable to locate applicable patch files, which by default
+                are <filename>*.patch</filename> or
+                <filename>*.diff</filename> files, or any file if
+                "apply=yes" is specified for the file in
+                <filename>SRC_URI</filename>.
+            </para>
+
+            <para>
+                BitBake finds and applies multiple patches for a single recipe
+                in the order in which it finds the patches.
+                Patches are applied to the recipe's source files located in the
+                <link linkend='var-S'><filename>S</filename></link> directory.
+            </para>
+
+            <para>
+                For more information on how the source directories are
+                created, see the
+                "<link linkend='source-fetching-dev-environment'>Source Fetching</link>"
+                section.
+            </para>
+        </section>
     </section>
 </section>