DOCS: update  encoding profiles installation instructions

Simply removed the assumption that the user is using `mpv-build`. Now provide 3
lines of shell that can be copy-pasted by the user for instant gratification
(and independent from $PWD).
cocoa_events: remove this functionality

This functionality looked smart but created problems with some kinds of
multi touch events. Moreover some events coming from the windows server – like
hovering a corner for window resize – didn't cause the player to wake up
immediately.

The "correct" non hacky way to implement async event polling with cocoa would
be having the vanilla cocoa event loop driving the player and setting up mpv's
terminal FDs as event sources for the cocoa event loop.

Fixes #20