README: remove legacy "for the command line" description

 Remove legacy description of MPV which does not reflect current
 reality, and the evolution into a GUI-ready player.

Signed-off-by: Bergmann Atmet <BergmannAtmet@github>

Author: Bergmann Atmet

README.md

@@ -28,7 +28,7 @@
 ## Overview
 
 
-**mpv** is a free (as in freedom) media player for the command line. It supports
+**mpv** is a free (as in freedom) modern GUI-ready media player. It supports
 a wide variety of media file formats, audio and video codecs, and subtitle types.
 
 There is a [FAQ][FAQ].