Add required scope for `public_github_token`

[Paulchen5]

When using your action on GitHub enterprise servers the action requires public_github_token to be set if I understood it correctly.

However I didn't found any specification which scopes the token needs. Please correct me / close the issue if I am wrong.

[emcfarlane]

Hey @Paulchen5 I've made a PR to improve the docs. The public_github_token needs access to the buf repository to download the release binary. This isn't needed if you don't require the action to install buf for you.

[Paulchen5]

Hi, thanks for your help.👍