docs(readme): add missing permission for delete-branch option in readme

[dan-pavlov]

Changes

• add missing contents: write permission to delete-branch option in readme

Context

Updating readme to include a permission that is required for delete-branch option that is missing from the readme. Configuring this workflow with that additional permission should prevent issues like #587 from being raised again (#587 wasn't actually resolved, just closed by a bot due to inactivity).

I have recently implemented this workflow in a repository configured with delete-branch: true. After the initial wait period, it started closing stale pull requests, but kept failing when trying to delete corresponding branches with the following error Error when deleting the branch "BRANCH_NAME" from pull request: Resource not accessible by integration.

Searching for answers I found the issue #587 mentioned above, where someone had the same problem, however no solution was provided there. Looking through the code, I found that this step is executed with the deleteRef action of the Octokit library, which in turn makes a request to the following GitHub REST API delete reference endpoint. According to GitHub REST API docs, that endpoint requires contents: write permission.

As the recommended permissions mentioned in Stale readme are set to issues: write and pull-requests: write, any other permissions that are absent from the list are set to none, therefore blocking delete-branch step from successfully executing.

After adding contents: write permission to the workflow configuration, when Stale workflow closed the next stale pull request, it successfully deleted the corresponding branch.

[davorpa]

Looks reasonable to me