binman: Incorporate entry documentation

Update this to avoid sphinx warnings and incorporate it into the new
documentaiton tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/cmdline.py b/tools/binman/cmdline.py
index 0c0f489..95f9ba2 100644
--- a/tools/binman/cmdline.py
+++ b/tools/binman/cmdline.py
@@ -69,7 +69,7 @@
         default=False, help='Update the binman node with offset/size info')
 
     entry_parser = subparsers.add_parser('entry-docs',
-        help='Write out entry documentation (see README.entries)')
+        help='Write out entry documentation (see entries.rst)')
 
     list_parser = subparsers.add_parser('ls', help='List files in an image')
     list_parser.add_argument('-i', '--image', type=str, required=True,