Update usage example for PRs originating in forks

[msfjarvis]

GitHub severely limits what access the default GITHUB_TOKEN for a PR originating from a fork has, which prevents the default configuration of this action from successfully posting the report as a PR comment. You can see an example failure here.

The README should be updated so that the example also works for this scenario.

[mi-kas]

Thanks @msfjarvis for pointing this issue out! I am afraid that github only allows read access for pull requests from
public forked repositories and unfortunately there is no way arround this (see permissions for Maximum access for pull requests from public forked repositories here: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token).

I will update the readme and mention this limitation.

[mi-kas]

Closed by 44e3c05