updating image name in the README

Author: cremuzzi

README.md

@@ -12,7 +12,7 @@ docker run --rm -i -t \
     -v /run/user/1000/pulse:/run/user/1000/pulse \
     -v $HOME/.Xauthority:/home/mpv/.Xauthority \
     -v /path/to/your/media/:/home/mpv/media:ro \
-    mpv
+    cremuzzi/mpv
 ```
 
 where `/path/to/your/media` is the directory of the media files that you want to play.