Document what permissions are needed for a PAT

[klauern]

Description

The documentation doesn't explain very well what permissions you need to grant a Personal Access Token in order to have it work with your tool. More specific documentation around what permissions need to be granted, perhaps with a screenshot of the checkboxes, would be ideal.

Reasons

When it errors, it does not specify what permissions are needed, so remediating this becomes a process of trial-and-error to add more permissions to a token than is probably necessary, just to have it be able to pass one of the checks.

[mszostok]

Hi :)
Documentation was added and merge to master:
https://github.com/mszostok/codeowners-validator/blob/master/docs/gh-token.md

if sth will be unclear/missing then please reopen the issue :)