Add a note that file:/// URLs will not work
Add a note that file:/// URLs will not work

Closes #543

Change-Id: I17821c780717eb53ede6653cf9645ffda923df7c

shaka-project/shaka-player,russitto/shaka-player,russitto/shaka-player,Ross-cz/shaka-player,TheModMaker/shaka-player,Ross-cz/shaka-player,TheModMaker/shaka-player,indiereign/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,vimond/shaka-player,vimond/shaka-player,brightcove/shaka-player,brightcove/shaka-player,TobbeEdgeware/shaka-player,TobbeEdgeware/shaka-player,indiereign/shaka-player,vimond/shaka-player,russitto/shaka-player,brightcove/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,indiereign/shaka-player,tvoli/shaka-player,tvoli/shaka-player,TobbeEdgeware/shaka-player,TheModMaker/shaka-player,Ross-cz/shaka-player,shaka-project/shaka-player