Should have instructions in README about required Github Action permission

[alank-ps]

This github action should mention requirements about permission.

Context

In #624 (comment), it seems checks: write is required

Current Behavior

No instructions in README and workflows will fail with resource are not accessible by integration

Expected Behavior

Users should be informed about required permissions

[dynaum]

I went through the same issue recently, and in my case, I also needed to add contents: read

[teolemon]

Created a PR for this: #678

[colleenjhardie]

I've reviewed @teolemon's PR. It solves this issue, but I don't have write access. Thanks for this! It helped me solve my issue today.