Add ticket triage role to dev guide

[maylee]

Ticket triage is a weekly, informal ritual that keeps tickets from getting lost in "ticket noise" and possibly opens up the possibility for exploring the decisions and philosophies relating to a ticket or, if the mood fits, "ticket heckling."

Regular ticket triage provides reconnaissance on the project's current priorities and prevents crufty build up.

The ticket triage person is a role that rotates weekly. The guidelines should be captured in a new file docs/ticket-triage.rst

• Person needs admin status
• Custom query the list of tickets for the last week (or other time frame)
  • BONUS: play "ticket roulette" and dig up some stale tickets
• Assign each ticket to a milestone on the Roadmap
  • Person can use their discretion to create appropriate milestones, if none exists
• If a ticket is unassignable, or merits discussion, person will bring up that ticket at the next meeting.
  • Ideally this meeting is the one that has the most regular attendance by core devs, currently Tuesday's meeting

[maylee]

Also have the option to close a ticket, because some tickets probably should really be closed.

[exarkun]

Person can use their discretion to create appropriate milestones, if none exists

I think new milestone creation should be more of a group effort.

[exarkun]

Fixed in ​https://github.com/tahoe-lafs/tahoe-lafs/commit/ff0f00f