Add a maintainer entry profile for documentation

Documentation should lead by example, so here's a basic maintainer entry
profile for this subsystem.

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/doc-guide/index.rst

@@ -11,6 +11,7 @@ How to write kernel documentation
    kernel-doc
    parse-headers
    contributing
+   maintainer-profile
 
 .. only::  subproject and html