init (wrapper): Note that -m is now deprecated

If the manifest format isn't XML, this option isn't available.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/repo b/repo
index 1374255..f73fa58 100755
--- a/repo
+++ b/repo
@@ -114,7 +114,8 @@
                  help='manifest branch or revision', metavar='REVISION')
 group.add_option('-m', '--manifest-name',
                  dest='manifest_name',
-                 help='initial manifest file', metavar='NAME.xml')
+                 help='initial manifest file (deprecated)',
+                 metavar='NAME.xml')
 group.add_option('--mirror',
                  dest='mirror', action='store_true',
                  help='mirror the forrest')