ref-manual: Added directfb to DISTRO_FEATURES list chapter.

Reported-by: Ross Burton <ross.burton@intel.com>
(From yocto-docs rev: c646f87697edaa18266e18c8608a91444930be6a)

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

documentation/ref-manual/ref-features.xml

@@ -78,6 +78,9 @@
                     bluetooth support (integrated BT only).</para></listitem>
                 <listitem><para><emphasis>cramfs:</emphasis> Include CramFS
                     support.</para></listitem>
+                <listitem><para><emphasis>directfb:</emphasis>
+                    Include DirectFB support.
+                    </para></listitem>
                 <listitem><para><emphasis>ext2:</emphasis> Include tools for
                     supporting for devices with internal HDD/Microdrive for
                     storing files (instead of Flash only devices).