MAINTAINERS: Add "R:" designated-reviewers tag

A ksummit-discuss email thread looked at the difficulty recruiting
and retaining reviewers.  Paul Walmsley also noted the need for patch
submitters to know who the key reviewers are and suggested adding an
"R:" tag to the MAINTAINERS file to record this information on a
per-subsystem basis.  This commit does just that, and a subsequent
commit tags the designated reviewer for the RCU-related subsystems.

http://lists.linuxfoundation.org/pipermail/ksummit-discuss/2014-May/000830.html

Suggested-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>

MAINTAINERS

@@ -70,6 +70,8 @@ Descriptions of section entries:
 
 	P: Person (obsolete)
 	M: Mail patches to: FullName <address@domain>
+	R: Designated reviewer: FullName <address@domain>
+	   These reviewers should be CCed on patches.
 	L: Mailing list that is relevant to this area
 	W: Web-page with status/info
 	Q: Patchwork web based patch tracking system site