Add reference information to README.md
Add reference information to README.md

tylingsoft/dagre-layout,abduld/dagre,tylingsoft/dagre-layout,dominiek/dagre-d3,9n/dagre,9n/dagre,rwl/graphlib_dot,abduld/dagre,harsha-mudi/dagre-d3,cpettitt/graphlib-dot,lmcorbo/dagre,cpettitt/dagre,GerHobbelt/dagre,git-ashish/dagre-d3,git-ashish/dagre-d3,cbfx/dagre-d3,abduld/dagre,cpettitt/dagre-d3,cpettitt/graphlib-dot,cpettitt/dagre,lmcorbo/dagre,GerHobbelt/dagre,cbfx/dagre-d3,leMaik/graphlib-dot,cpettitt/dagre,9n/dagre-d3,rwl/dagre_charted,dominiek/dagre-d3,rwl/dagre_charted,git-ashish/dagre-d3,kdawes/dagre,rwl/dagre_charted,cpettitt/dagre-d3,shelsonjava/dagre,cpettitt/dagre-d3,rwl/dagre,9n/dagre-d3,shelsonjava/dagre,harsha-mudi/dagre-d3,9n/dagre-d3,witcxc/dagre,ENCODE-DCC/dagre-d3,dagrejs/dagre-d3,kdawes/dagre,lmcorbo/dagre,kdawes/dagre,dominiek/dagre-d3,GerHobbelt/dagre,ENCODE-DCC/dagre-d3,shelsonjava/dagre,leMaik/graphlib-dot,9n/dagre,cbfx/dagre-d3,dagrejs/dagre-d3,witcxc/dagre