Allow un-ToS'd users to view other Legalpad documents

Summary:
Fixes T7420. On Phacility, our ToS currently links to some policy documents, but users who haven't signed the ToS can't see them.

I've just created a blanket exemption and documented it; I think this is reasonable in all cases.

Test Plan: As an un-ToS'd user, viewed some other documents.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7420

Differential Revision: https://secure.phabricator.com/D11923