Document ACCESS_TOKEN required scope

[hsz]

Is your feature request related to a problem? Please describe.

There is no information about the required scope for the ACCESS_TOKEN.

Describe the solution you'd like

Describe which parts of the scope are needed.

[JamesIves]

I added a note about it in the variables table. The actual scope type will depend on the type of repository the action is being used in. Private read/write if the repository is private, public if it's public, etc.

Keep in mind that once #13 merges the access token will be somewhat obsolete (although it will still work for redundancy) as the GITHUB_TOKEN is correctly scoped to the repository which invoked the action.