add cargo doc to README
add cargo doc to README

carck/async,suguru03/async,rborisov/async,chaddm/async,chaddm/async,haggholm/async,evdevgit/async,KnottedRain/async,ibakaidov/async,renruixi/async,ibakaidov/async,ezubarev/async,DanieleTassone/async,KnottedRain/async,megawac/async,markyen/async,bjlxj2008/async,steverobb/async,DanieleTassone/async,jnordberg/async,kolomiichenko/async,justincy/async,rlugojr/async,XM-Right/async,llwanghong/async,Connectlegendary/async,steverobb/async,andalm/async,Kikobeats/async,yaronn/async,FrankSunnyvale/async,Segeon-Kim/async,arigo-software/async,imjerrybao/async,megawac/async,LeoYao/async,ariesnah/async,pandoraui/async,suguru03/async,wrenth04/async,modulexcite/async,mingqi/uclogs-async,Connectlegendary/async,zhakui/async,navyxie/async,ecasilla/async,haggholm/async,xiebaochun/async,DDunc/async,youprofit/async,scq000/async,wushuyi/async,moander/async,hargasinski/async,lonely8rain/async,lanffy/async,Segeon-Kim/async,ariesnah/async,mcanthony/async,Kikobeats/async,JulianVolodia/async,justincy/async,mcanthony/async,jaruba/async,modulexcite/async,Qix-/async,Zhang/async,caolan/async,DaAwesomeP/async,r14r-work/fork_javascript_async,ezubarev/async,ArcadiusK/async,lanffy/async,r14r-work/fork_javascript_async,RickyDan/async,FrankSunnyvale/async,mikedeboer/mozAsync,imjerrybao/async,caolan/async,wushuyi/async,beni55/async,hargasinski/async,rlugojr/async,llwanghong/async,r14r/fork_javascript_async,ArcadiusK/async,pandeysoni/async,pandoraui/async,garysye/async,sjclijie/async,SaiNadh001/async,andalm/async,Qix-/async,zhhb/async,moander/async,zhhb/async,tjwudi/async,bjlxj2008/async,abhishekgahlot/async,arigo-software/async,scq000/async,LeoYao/async,XM-Right/async,rborisov/async,virtdb/async,renruixi/async,DaAwesomeP/async,mingqi/uclogs-async,DDunc/async,r14r/fork_javascript_async,wrenth04/async,andyburke/antisync,garysye/async,kolomiichenko/async,RickyDan/async,JulianVolodia/async,beni55/async,tjwudi/async,evdevgit/async,gypsydave5/async,jamesjnadeau/async,Segeon-Kim/async,navyxie/async,Zhang/async,sjclijie/async,xiebaochun/async,jaruba/async,carck/async,andyburke/antisync,markyen/async,zhakui/async,ecasilla/async,jamesjnadeau/async,SaiNadh001/async,gypsydave5/async,lonely8rain/async,abhishekgahlot/async,jnordberg/async,youprofit/async,pandeysoni/async