ref-manual: Added cross-reference link to term "Metadata".

(From yocto-docs rev: a182cae60ccddfc881eb5c835dbb64db84f6d733)

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

documentation/ref-manual/ref-classes.xml

@@ -335,7 +335,9 @@
         This comparison takes into account a complete build of the package with all
         dependencies previously built.
         The reason for this discrepancy is because the RPM package manager creates and
-        processes more metadata than the IPK package manager.
+        processes more 
+        <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> than the 
+        IPK package manager.
         Consequently, you might consider setting <filename>PACKAGE_CLASSES</filename>
         to "package_ipk" if you are building smaller systems.
     </para>