updated add-on description
updated add-on description

davidjb/browser-media-keys,miicha/browser-media-keys,gmelikov/browser-media-keys,davidjb/browser-media-keys,carlin-q-scott/browser-media-keys,carlin-q-scott/browser-media-keys,miicha/browser-media-keys,gmelikov/browser-media-keys,gmelikov/browser-media-keys