Update README.md (#262)

README.md

@@ -39,7 +39,7 @@ Retrieve all changed files relative to the default branch (`pull_request*` based
 >
 > *   **IMPORTANT:** For `push` events you need to include `fetch-depth: 0` **OR** `fetch-depth: 2` depending on your use case.
 > *   When using `persist-credentials: false` with `actions/checkout@v2` you'll need to specify a `token` using the `token` input.
-> *   For monorepos were pulling all the branch history might not be desired the `fetch-depth` can be omitted.
+> *   For monorepos were pulling all the branch history might not be desired the `fetch-depth` can be omitted for `pull_request` events.
 
 ```yaml
 name: CI