* readme.md: reincarnate wiki

It is kinda strange to announce that wiki is deprecated, while it is in fact growing.
I'd say, the "Move-the-wiki" milestone is stalled instead.

* Readme.md: rename to community maintained wiki

This makes them look consistent with the travis badge.

We probably no longer want to advertise it.

Turns out it was already up to date and I just had a stale cache!

Seems like the community was in support of changing it, and someone went and changed it on the homepage, so we might as well stay consistent.

@vcunat dropped `Main_Page` suffix from the link.

(cherry picked from commit 78bb17dd22e4da4e3810fbc78185d73bb25ea73e)
Signed-off-by: Domen Kožar <domen@dev.si>