Point "Policy and Rules" for Developer Agreement to ATN Review Policy

[ryanleesipes]

Currently on the add-on submission agreement page, the "Review Policies and Rules" points at: https://addons.thunderbird.net/en-US/developers/docs/policies/reviews

It should point at the Thunderbird Review policy: https://thundernest.github.io/atn-review-policy

However, this is not localized, so open to suggestions to accomplish that. But it has diverged from Mozilla's.