Inform users that VP9 may be hardware accelerated.

[Poopooracoocoo]

Inform users in the README or otherwise that VP9 (and AV1, among other codecs) may be decoded by their hardware

Users can check this in Chromium based browsers including Chrome by navigating to chrome://gpu and then going to the 'video acceleration information' and viewing the table of codecs that are hardware accelerated on the system.

There must be a way to do so in Firefox.