readme: Mention the go 1.6 requirement in the README for building runc
readme: Mention the go 1.6 requirement in the README for building runc

Signed-off-by: Mrunal Patel <d389837b018b67489df74a2c5f0aca13aaed44b6@gmail.com>

shishir-a412ed/runc,stefanberger/runc,coolljt0725/runc,rajasec/runc,wking/runc,nkwilson/runc,opencontainers/runc,xiaochenshen/runc,cyphar/runc,avagin/runc,mheon/runc,maxamillion/runc,keloyang/runc,docker/runc,justincormack/runc,rhatdan/runc,dqminh/runc,kolyshkin/runc,hqhq/runc,cloudfoundry-incubator/runc,xiaochenshen/runc,nkwilson/runc,rhatdan/runc,rhatdan/runc,avagin/runc,justincormack/runc,cloudfoundry-incubator/runc,hqhq/runc,wking/runc,mikebrow/runc,mikebrow/runc,kolyshkin/runc,dqminh/runc,estesp/runc,adrianreber/runc,xiaochenshen/runc,shishir-a412ed/runc,adrianreber/runc,crosbymichael/runc,sunyuan3/runc,mYmNeo/runc,WeiZhang555/runc,wking/runc,keloyang/runc,stefanberger/runc,laijs/runc,vbatts/runc,jhowardmsft/runc,jhowardmsft/runc,dqminh/runc,jhowardmsft/runc,crosbymichael/runc,docker/runc,mikebrow/runc,maxamillion/runc,kolyshkin/runc,estesp/runc,stefanberger/runc,cyphar/runc,cyphar/runc,vbatts/runc,rhatdan/runc,laijs/runc,nkwilson/runc,mYmNeo/runc,justincormack/runc,kolyshkin/runc,coolljt0725/runc,opencontainers/runc,maxamillion/runc,keloyang/runc,rajasec/runc,adrianreber/runc,coolljt0725/runc,dqminh/runc,docker/runc,opencontainers/runc,cloudfoundry-incubator/runc,hqhq/runc,avagin/runc,crosbymichael/runc,opencontainers/runc,mYmNeo/runc,sunyuan3/runc,mheon/runc,sunyuan3/runc,WeiZhang555/runc,estesp/runc,shishir-a412ed/runc,mheon/runc,laijs/runc,rajasec/runc,vbatts/runc,WeiZhang555/runc