Duplicate Media Sessions

[Iwaslazkis]

With this extensions, I'm not sure I really need the browser MPRIS media session anymore. It may be useful to disable the default mpris provider in the browser, and add instructions to README.md. Based off the comments in this issue, it seems this can be done by disabling either enable-media-session-service or hardware-media-key-handling flags.

That said, I'm not sure if we really want to entirely disable this, since some other websites not supported by this extension may also use the media controls, at which point the broken chromium interface is better than nothing, like Soundcloud or the Free Music Archive. So, ideally we would turn it off specifically for websites like YouTube for which this extension already supports... Not really sure how one would implement that though.