Add manifest file.

manifest.yaml

@@ -0,0 +1,8 @@
+
+hooks:
+    -
+        id: validate_manifest
+        name: Validate Manifest
+        description: This validator validates a pre-commit hooks manifest file
+        entry: validate-manifest
+        language: python

pre_commit/clientlib/validate_manifest.py

@@ -61,8 +61,8 @@ validate_manifest = get_validator(
 def run(argv):
     parser = argparse.ArgumentParser()
     parser.add_argument(
-        '--filename',
-        required=False, default=None,
+        'filename',
+        nargs='?', default=None,
         help='Manifest filename.  Defaults to {0} at root of git repo'.format(
             C.MANIFEST_FILE,
         )