patman: Add documentation to doc/

Link to patman's documentation from the doc/ directory so that it appears
in the 'make htmldocs' output.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/tools/patman/main.py b/tools/patman/main.py
index 15e7af0..5a7756a 100755
--- a/tools/patman/main.py
+++ b/tools/patman/main.py
@@ -164,7 +164,8 @@
 
     elif args.full_help:
         tools.print_full_help(
-            os.path.join(os.path.dirname(os.path.realpath(sys.argv[0])), 'README')
+            os.path.join(os.path.dirname(os.path.realpath(sys.argv[0])),
+                         'README.rst')
         )
 
     else: