Add missing parameter --allow-missing-credentials

Author: rpdelaney

README.md

@@ -61,6 +61,8 @@ Add this to your `.pre-commit-config.yaml`
   - `--credentials-file` - additional AWS CLI style configuration file in a
     non-standard location to fetch configured credentials from. Can be repeated
     multiple times.
+  - `--allow-missing-credentials` - Allow hook to pass when no credentials are
+    detected.
 - `detect-private-key` - Checks for the existence of private keys.
 - `double-quote-string-fixer` - This hook replaces double quoted strings
   with single quoted strings.