Fix external subtitles example

Currently, running the example results in:

> TypeError: MPV.play() got an unexpected keyword argument 'sub_file'

1 files changed, 2 insertions, 1 deletions

diff --git a/README.rst b/README.rst
index 3af7d9d..1f61efe 100644
--- a/README.rst
+++ b/README.rst
@@ -241,7 +241,8 @@ The easiest way to load custom subtitles from a file is to pass the ``--sub-file
     import mpv
 
     player = mpv.MPV()
-    player.play('test.webm', sub_file='test.srt')
+    player.loadfile('test.webm', sub_file='test.srt')
+    player.wait_for_playback()
 
 Note that you can also pass many other options to ``loadfile``. See the mpv docs for details.