Add instructions for new fine grained GitHub PAT

Author: ibizaman

README.md

@@ -185,7 +185,7 @@ git push origin update_flake_lock_action --force
 ### With a Personal Authentication Token
 
 By providing a Personal Authentication Token, the PR will be submitted in a way that bypasses this limitation (GitHub will essentially think it is the owner of the PAT submitting the PR, and not an Action).
-You can create a token by visiting https://github.com/settings/tokens and select at least the `repo` scope. Then, store this token in your repository secrets (i.e. `https://github.com/<USER>/<REPO>/settings/secrets/actions`) as `GH_TOKEN_FOR_UPDATES` and set up your workflow file like the following:
+You can create a token by visiting https://github.com/settings/tokens and select at least the `repo` scope. For the new fine-grained tokens, you need to enable read and write access for "Contents" and "Pull Requests" permissions. Then, store this token in your repository secrets (i.e. `https://github.com/<USER>/<REPO>/settings/secrets/actions`) as `GH_TOKEN_FOR_UPDATES` and set up your workflow file like the following:
 
 ```yaml
 name: update-flake-lock