ref-manual: Created new "Closer Look" chapter

Fixes [YOCTO #2808]

I extracted the section that takes a closer look at the YP
development process into its own chapter.  Feedback during the
review indicated that this information should not be buried as
it was in a section but rather pulled higher out for visibility.

So, The changes create a new chapter three that is dedicated to
this topic.

(From yocto-docs rev: 32c66976b6b84787d14d6174dab843862a0d184b)

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

documentation/ref-manual/ref-manual.xml

@@ -99,6 +99,8 @@
 
     <xi:include href="usingpoky.xml"/>
 
+    <xi:include href="closer-look.xml"/>
+
     <xi:include href="technical-details.xml"/>
 
     <xi:include href="migration.xml"/>