Update fetchart documentation.
Update fetchart documentation.

pkess/beets,lengtche/beets,sampsyo/beets,MyTunesFreeMusic/privacy-policy,beetbox/beets,xsteadfastx/beets,Freso/beets,beetbox/beets,sampsyo/beets,sampsyo/beets,mosesfistos1/beetbox,xsteadfastx/beets,ibmibmibm/beets,jackwilsdon/beets,diego-plan9/beets,beetbox/beets,madmouser1/beets,xsteadfastx/beets,artemutin/beets,Kraymer/beets,xsteadfastx/beets,madmouser1/beets,madmouser1/beets,lengtche/beets,artemutin/beets,lengtche/beets,jcoady9/beets,mosesfistos1/beetbox,Freso/beets,SusannaMaria/beets,jackwilsdon/beets,shamangeorge/beets,Freso/beets,jackwilsdon/beets,jackwilsdon/beets,shamangeorge/beets,lengtche/beets,SusannaMaria/beets,artemutin/beets,SusannaMaria/beets,MyTunesFreeMusic/privacy-policy,artemutin/beets,diego-plan9/beets,beetbox/beets,MyTunesFreeMusic/privacy-policy,Kraymer/beets,mosesfistos1/beetbox,Freso/beets,shamangeorge/beets,pkess/beets,SusannaMaria/beets,ibmibmibm/beets,diego-plan9/beets,Kraymer/beets,shamangeorge/beets,jcoady9/beets,ibmibmibm/beets,pkess/beets,pkess/beets,Kraymer/beets,sampsyo/beets,mosesfistos1/beetbox,madmouser1/beets,jcoady9/beets,MyTunesFreeMusic/privacy-policy,jcoady9/beets,diego-plan9/beets,ibmibmibm/beets