docs: GITHUB_RUN_ID set by default

although this is not documented in the github api :eyeroll:

README.md

@@ -10,15 +10,14 @@ GitHub actions.
 
 None. The action uses the GitHub action environment variables
 to obtain the workflow name and branch. You must, however,
-set the `GITHUB_TOKEN` and `GITHUB_RUN_ID` environment variables:
+set the `GITHUB_TOKEN` environment variable:
 
 ## Example usage
 
 ```yaml
 uses: rokroskar/workflow-run-cleanup-action
 env:
   GITHUB_TOKEN: ${{ secret.GITHUB_TOKEN }}
-  GITHUB_RUN_ID: ${{ github.run_id }}
 ```
 
 You may want to disable this action from running on tags or master,
@@ -36,7 +35,6 @@ on:
       - uses: rokroskar/workflow-run-cleanup-action@master
         env:
           GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
-          GITHUB_RUN_ID: ${{ github.run_id }}
       if: "!startsWith(github.ref, 'refs/tags/') && github.ref != 'refs/heads/master'"
     ...
     other-jobs: