dev-manual: Added new "writernotes" style.

This style is for review purposes and can be implemented in
the XML file using <para role='writernotes'>.  The text in the
paragraph is rendered red.

(From yocto-docs rev: db990802594af3a70b11e320c06fe6a9dc80579b)

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

documentation/dev-manual/dev-style.css

@@ -730,6 +730,10 @@ div.navfooter {
   border-color: black;
 }
 
+.writernotes {
+  color: red;
+}
+
 
   /*********** /
  /  graphics  /