docs(custom-resources): update resource policy description (aws#8222)

Commit Message
----
documentation issue
 fixes [aws#8157](aws#8157)

End Commit Message
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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

CONTRIBUTING.md

@@ -234,7 +234,7 @@ BREAKING CHANGE: Description of what broke and how to achieve this behavior now
 ### Step 5: Pull Request
 
 * Push to a GitHub fork or to a branch (naming convention: `<user>/<feature-bug-name>`)
-* Submit a Pull Requests on GitHub and assign the PR for a review to the "awslabs/aws-cdk" team.
+* Submit a Pull Request on GitHub. A reviewer will later be assigned by the maintainers.
 * Please follow the PR checklist written below. We trust our contributors to self-check, and this helps that process!
 * Discuss review comments and iterate until you get at least one “Approve”. When iterating, push new commits to the
   same branch. Usually all these are going to be squashed when you merge to master. The commit messages should be hints

packages/@aws-cdk/custom-resources/lib/aws-custom-resource/aws-custom-resource.ts

@@ -205,7 +205,8 @@ export interface AwsCustomResourceProps {
   readonly onDelete?: AwsSdkCall;
 
   /**
-   * The policy to apply to the resource.
+   * The policy that will be added to the execution role of the Lambda
+   * function implementing this custom resource provider.
    *
    * The custom resource also implements `iam.IGrantable`, making it possible
    * to use the `grantXxx()` methods.