new meetup policy: promote posts only with first-time meetups

I propose for comment the following alteration of the LW meetup promotion policy:

* The weekly meetup roundup will contain, in its title, only the names of cities which have not previously had an LW meetup, or which have not had an LW meetup in the last year.

* On occasions where no such name appears in the title, the meetup roundup post will still appear in Main but will not be Promoted.

* Cities having a first-time meetup, or where a new meetup is being started by a new organizer after a hiatus, should have additional info about that meetup and its organizer appearing in a prominent, top-of-post position in the roundup post.

This is intended to make it easier for new meetups to gain attention, by requiring hopeful LWers awaiting a new meetup in their area to pay attention to a smaller number of promoted posts and a smaller number of cities appearing in the titles of Main posts.