Add project tag mpv-script

[stax76]

I suggest adding the tag mpv-script because tags are an excellent way to find software.

https://github.com/topics/mpv-script

[Eisa01]

Thanks for the tip, I'll see how it can be added.

[stax76]

You can add it very easily via UI on the main readme page.

It's in the same dialog where you can edit the page about title.

[Eisa01]

Done