Update README with testing instructions.
Update README with testing instructions.

crazypenguincode/vimium,decaffeinate-examples/vimium,cyrixhero/vimium,gdh1995/vimium,Robinson10240/vimium,smblott-github/vimium-smblott,Aleroniponi/vimium,PickRelated/vimium,bkudria/vimium,VPashkov/vimium,borgified/vimium,cyrixhero/vimium,Lw-Cui/vimium,smblott-github/vimium-smblott,poacher2k/vimium,mrmr1993/vimium,wildeyes/vimium,tuchangwei/vimium,gdh1995/vimium,borgified/vimium,elegantwww/vimium,borgified/vimium,PickRelated/vimium,PickRelated/vimium,decaffeinate-examples/vimium,elderbas/vimium,zhangmin510/vimium,Robinson10240/vimium,jb55/vimium-plus,smblott-github/vimium,poacher2k/vimium,cyrixhero/vimium,elderbas/vimium,wildeyes/vimium,justalittlenoob/vimium,PrestanceDesign/vimium,justalittlenoob/vimium,douglas-larocca/vimium,bkudria/vimium,willsALMANJ/vimium,douglas-larocca/vimium,dimatter/vimium,justalittlenoob/vimium,wildeyes/vimium,csmalin/vimium,jb55/vimium-plus,douglas-larocca/vimium,hhsue/vimium,philc/vimium,smblott-github/vimium,hhsue/vimium,VPashkov/vimium,poacher2k/vimium,Lw-Cui/vimium,philc/vimium,Robinson10240/vimium,dimatter/vimium,elegantwww/vimium,decaffeinate-examples/vimium,tuchangwei/vimium,crazypenguincode/vimium,bkudria/vimium,Aleroniponi/vimium,gdh1995/vimium,csmalin/vimium,hhsue/vimium,dimatter/vimium,elegantwww/vimium,zhangmin510/vimium,mrmr1993/vimium,Lw-Cui/vimium,csmalin/vimium,PrestanceDesign/vimium,mrmr1993/vimium,Aleroniponi/vimium,smblott-github/vimium,PrestanceDesign/vimium,tuchangwei/vimium,zhangmin510/vimium,elderbas/vimium,willsALMANJ/vimium,philc/vimium,willsALMANJ/vimium,VPashkov/vimium