buildman: Convert documentation to rST

Convert the buildman documentation to rST format and include it in the
'build' section.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Quentin Schulz <foss+uboot@0leil.net>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 0c75466..377b580 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -136,8 +136,8 @@
 
     if options.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'))
         return 0
 
     gitutil.setup()