Add subs to `subs`!

[BachoSeven]

Hi, I noticed that mpv automatically loads the embedded subtitles from youtube videos which have them, but does not select them automatically.

I would add it to the README that you can add --sid=1 to the command line options, or sid=1 to ~/.config/mpv/mpv.conf in order to select the first available subtitles. Of course, if there are multiple languages, one can always switch between those using j and J, or turn them off with v.

I think that would be an helpful tip to mention!

[BachoSeven]

ok i realised this is not actually that useful nor related to the program, closing.