add docs for delta api
add docs for delta api

voxmedia/quill,tim-mc/quill,sferoze/quilljs,willrowe/quill,tim-mc/quill,sferoze/quilljs,willrowe/quill,quilljs/quill,voxmedia/quill,sferoze/quilljs,sferoze/quilljs,voxmedia/quill,willrowe/quill,quilljs/quill,quilljs/quill