Document `GITHUB_TOKEN` settings - Cypress Cloud recording

## What would you like?

Document the necessary permission settings for `GITHUB_TOKEN`.

## Why is this needed?

As documented in the README [Automatic PR number and URL detection](https://github.com/cypress-io/github-action/blob/master/README.md#automatic-pr-number-and-url-detection), if the `GITHUB_TOKEN` is set when recording to Cypress Cloud, PR information is extracted.

Restrictive [permissions for the GITHUB_TOKEN](https://docs.github.com/en/actions/security-for-github-actions/security-guides/automatic-token-authentication#permissions-for-the-github_token) can however have been set in the enterprise, organization, repository or workflow which may prevent this working.

## Other

### Related issues

- https://github.com/cypress-io/github-action/issues/1208