Formally reject new protocols

[emersion]

New protocols should go in wayland-protocols' ext namespace, which has no more inclusion requirements than this repo, but also offers reviews by non-wlroots people and allows to host all protocols in the same place.

Proposal: reject new protocols in wlr-protocols. Only accept updates for protocols not yet included in wayland-protocols.

cc @ddevault

[agx]

This sounds good - maybe it would be good to mention how to do that in the README.md of this repo?

[ddevault]

ack