Document who has triage permissions

[vmbrasseur]

E.g., to add assignees and labels

This is related to #6, inasmuch as it's about who has what permissions on which repos (and how they get them).

[jniesz]

My thought is for right now have this the same as the committers and if a repo wants to have dedicated folks for triage (assign labels, manage pull requests, etc..) they can conduct a vote (majority) to assign specific people for triage role.

[vmbrasseur]

This seems reasonable.

This seems related to #8, so they can both be handled at once wrt documenting things.