readme

packages/aws-cdk/README.md

@@ -165,6 +165,8 @@ $ # Diff against the currently deployed stack with quiet parameter enabled
 $ cdk diff --quiet --app='node bin/main.js' MyStackName
 ```
 
+Note that the CDK::Metadata resource and the `CheckBootstrapVersion` Rule are excluded from `cdk diff` by default. You can force `cdk diff` to display them by passing the `--strict` flag.
+
 The `change-set` flag will make `diff` create a change set and extract resource replacement data from it. This is a bit slower, but will provide no false positives for resource replacement.
 The `--no-change-set` mode will consider any change to a property that requires replacement to be a resource replacement,
 even if the change is purely cosmetic (like replacing a resource reference with a hardcoded arn).