Add Appveyor Badge to readme.md (#741)
Add Appveyor Badge to readme.md (#741)

* Add Appveyor Badge to readme.md. Fixes issue #684.

librasungirl/openthread,GiedriusM/openthread,LeZhang2016/openthread,mszczodrak/openthread,JakubBrachTieto/openthread,nibanks/openthread,xiaom-GitHub/openthread,georgecpr/openthread,jjlee9/openthread,mszczodrak/openthread,chshu/openthread,vaas-krish/openthread,turon/openthread,LeZhang2016/openthread,openthread/openthread,fbsder/openthread,vaas-krish/openthread,jjlee3/openthread,georgecpr/openthread,lanyuwen/openthread,lanyuwen/openthread,xiaom-GitHub/openthread,turon/openthread,mszczodrak/openthread,openthread/openthread,xiaom-GitHub/openthread,xiaom-GitHub/openthread,gandreello/openthread,JakubBrachTieto/openthread,mszczodrak/openthread,librasungirl/openthread,nibanks/openthread,jjlee3/openthread,chshu/openthread,erja-gp/openthread,nibanks/openthread,GiedriusM/openthread,jjlee9/openthread,vaas-krish/openthread,fbsder/openthread,GiedriusM/openthread,gandreello/openthread,chshu/openthread,abtink/openthread,aeliot/openthread,chshu/openthread,mszczodrak/openthread,jwhui/openthread,aeliot/openthread,fbsder/openthread,erja-gp/openthread,jwhui/openthread,bukepo/openthread,pvanhorn/openthread,pvanhorn/openthread,abtink/openthread,jjlee9/openthread,vaas-krish/openthread,erja-gp/openthread,nibanks/openthread,pvanhorn/openthread,fbsder/openthread,JakubBrachTieto/openthread,GiedriusM/openthread,Zolertia/openthread,librasungirl/openthread,georgecpr/openthread,Zolertia/openthread,chshu/openthread,gandreello/openthread,xiaom-GitHub/openthread,LeZhang2016/openthread,nibanks/openthread,xiaom-GitHub/openthread,Zolertia/openthread,LeZhang2016/openthread,lanyuwen/openthread,erja-gp/openthread,openthread/openthread,openthread/openthread,nibanks/openthread,gandreello/openthread,aeliot/openthread,pvanhorn/openthread,fbsder/openthread,jwhui/openthread,Zolertia/openthread,aeliot/openthread,abtink/openthread,Zolertia/openthread,gandreello/openthread,JakubBrachTieto/openthread,bukepo/openthread,fbsder/openthread,bukepo/openthread,bukepo/openthread,jjlee9/openthread,lanyuwen/openthread,erja-gp/openthread,jjlee9/openthread,mszczodrak/openthread,pvanhorn/openthread,jjlee3/openthread,lanyuwen/openthread,LeZhang2016/openthread,jjlee3/openthread,vaas-krish/openthread,gandreello/openthread,georgecpr/openthread,srickardti/openthread,GiedriusM/openthread,LeZhang2016/openthread,turon/openthread,turon/openthread,jjlee3/openthread,pvanhorn/openthread,lanyuwen/openthread,librasungirl/openthread,aeliot/openthread,srickardti/openthread,georgecpr/openthread,erja-gp/openthread,JakubBrachTieto/openthread,srickardti/openthread,JakubBrachTieto/openthread,georgecpr/openthread,vaas-krish/openthread,jwhui/openthread,srickardti/openthread,aeliot/openthread,chshu/openthread,abtink/openthread,jjlee9/openthread