plugin: mention OS X support and concurrency
plugin: mention OS X support and concurrency

Change-Id: I4270bf81511a5bf80ed146f5e66e4f8aeede2aa2
Reviewed-on: https://go-review.googlesource.com/31463
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

momchil-velikov/go,momchil-velikov/go,Cofyc/go,derekmarcotte/go,cloudflare/go,CAFxX/go,linux-on-ibm-z/go,golang/go,goodlang/good,cloudflare/go,cloudflare/go,CAFxX/go,goodlang/good,nawawi/go,akutz/go,Cofyc/go,nawawi/go,polyverse-security/go,linux-on-ibm-z/go,akutz/go,nawawi/go,vsekhar/elastic-go,josharian/go,cloudflare/go,CAFxX/go,josharian/go,polyverse-security/go,golang/go,suncycheng/go,akutz/go,cloudflare/go,linux-on-ibm-z/go,codestation/go,vsekhar/elastic-go,suncycheng/go,polyverse-security/go,nawawi/go,ImJasonH/go,golang/go,momchil-velikov/go,CAFxX/go,Cofyc/go,nawawi/go,derekmarcotte/go,polyverse-security/go,derekmarcotte/go,polyverse-security/go,goodlang/good,josharian/go,cloudflare/go,ImJasonH/go,momchil-velikov/go,Cofyc/go,cloudflare/go,akutz/go,momchil-velikov/go,goodlang/good,nawawi/go,goodlang/good,codestation/go,akutz/go,codestation/go,derekmarcotte/go,golang/go,ImJasonH/go,ImJasonH/go,nawawi/go,josharian/go,Cofyc/go,josharian/go,ImJasonH/go,derekmarcotte/go,josharian/go,momchil-velikov/go,CAFxX/go,suncycheng/go,vsekhar/elastic-go,suncycheng/go,vsekhar/elastic-go,goodlang/good,akutz/go,momchil-velikov/go,codestation/go,cloudflare/go,derekmarcotte/go,Cofyc/go,vsekhar/elastic-go,josharian/go,Cofyc/go,vsekhar/elastic-go,golang/go,codestation/go,goodlang/good,vsekhar/elastic-go,ImJasonH/go,linux-on-ibm-z/go,golang/go,Cofyc/go,suncycheng/go,linux-on-ibm-z/go,derekmarcotte/go,linux-on-ibm-z/go,golang/go,linux-on-ibm-z/go,CAFxX/go,derekmarcotte/go,polyverse-security/go,ImJasonH/go,josharian/go,codestation/go,goodlang/good,ImJasonH/go,polyverse-security/go,golang/go,CAFxX/go,nawawi/go,suncycheng/go,codestation/go,codestation/go,vsekhar/elastic-go,suncycheng/go,akutz/go,momchil-velikov/go,suncycheng/go,polyverse-security/go,linux-on-ibm-z/go,akutz/go,christopher-henderson/Go,CAFxX/go