Added a note on scope
Added a note on scope

Picturefill aims to polyfill the standard features of the `picture` element and related `srcset`, `sizes`, `type`, and `media` attributes (some of which work on `img` elements without a `picture` parent as well). Issues and contributions that fall outside of this scope are not likely to be accepted by the project. Some exceptions include workarounds that improve browser support for standard features.
mcanthony/picturefill,ddeveloperr/picturefill,yufi113/picturefill,yufi113/picturefill,iancrowther/picturefill,patrickkettner/picturefill,chrismcandrew/picturefill,albell/picturefill,albell/picturefill,footiealf/picturefill,footiealf/picturefill,iancrowther/picturefill,samiadelgado/picturefill,rockmandew/picturefill,samiadelgado/picturefill,rockmandew/picturefill,chrismcandrew/picturefill,scottjehl/picturefill,scottjehl/picturefill,demateu/picturefill,mcanthony/picturefill,patrickkettner/picturefill,nucliweb/picturefill,demateu/picturefill,guardian/picturefill,guardian/picturefill,yubin-huang/picturefill,purposeindustries/picturefill,purposeindustries/picturefill,ddeveloperr/picturefill,yubin-huang/picturefill