cmd/cgo: clarify C.GoStringN and C.GoBytes docs
cmd/cgo: clarify C.GoStringN and C.GoBytes docs

Fixes #12427.

Change-Id: I46725620c1e163f3b60ffcd85e5388fa646f074d
Reviewed-on: https://go-review.googlesource.com/15997
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

fjballest/golang,Jordanzuo/go,odeke-em/go,golang/go,Samurais/go,momchil-velikov/go,cloudflare/go,sndnvaps/go,Endika/go,malvira/go,josharian/go,mwhudson/go,goodlang/good,4ad/go,Endika/go,fjballest/golang,codestation/go,codestation/go,polyverse-security/go,golang/go,akutz/go,ImJasonH/go,josharian/go,CAFxX/go,Endika/go,ganboing/go-esx,Jordanzuo/go,odeke-em/go,codestation/go,ganboing/go-esx,CAFxX/go,roth1002/go,derekmarcotte/go,CAFxX/go,theif519/go,Endika/go,Samurais/go,deft-code/go,akutz/go,cyberroadie/go,miolini/go,cyberroadie/go,sndnvaps/go,momchil-velikov/go,malvira/go,polyverse-security/go,gdey/go,goodlang/good,suncycheng/go,polyverse-security/go,golang/go,malvira/go,sndnvaps/go,gdey/go,ImJasonH/go,cyberroadie/go,miolini/go,gdey/go,roth1002/go,4ad/go,4ad/go,josharian/go,odeke-em/go,mwhudson/go,miolini/go,binarycrusader/go,akutz/go,linux-on-ibm-z/go,nawawi/go,codestation/go,Cofyc/go,malvira/go,nawawi/go,ImJasonH/go,polyverse-security/go,deft-code/go,Endika/go,Cofyc/go,codestation/go,odeke-em/go,rachtsingh/gogojuice,josharian/go,polyverse-security/go,Cofyc/go,binarycrusader/go,Samurais/go,roth1002/go,CAFxX/go,deft-code/go,linux-on-ibm-z/go,derekmarcotte/go,akutz/go,gdey/go,cyberroadie/go,ganboing/go-esx,mwhudson/go,nawawi/go,ImJasonH/go,cyberroadie/go,Cofyc/go,theif519/go,4ad/go,odeke-em/go,binarycrusader/go,cloudflare/go,deft-code/go,goodlang/good,miolini/go,Samurais/go,kim-racktop/go,gdey/go,malvira/go,vanloswang/go,binarycrusader/go,goodlang/good,mwhudson/go,golang/go,4ad/go,kim-racktop/go,mwhudson/go,josharian/go,cyberroadie/go,sndnvaps/go,ganboing/go-esx,CAFxX/go,momchil-velikov/go,vanloswang/go,ganboing/go-esx,theif519/go,derekmarcotte/go,malvira/go,roth1002/go,cyberroadie/go,sndnvaps/go,Jordanzuo/go,suncycheng/go,gdey/go,cloudflare/go,vanloswang/go,Jordanzuo/go,Jordanzuo/go,Jordanzuo/go,kim-racktop/go,suncycheng/go,ImJasonH/go,roth1002/go,deft-code/go,ganboing/go-esx,binarycrusader/go,odeke-em/go,cloudflare/go,nawawi/go,miolini/go,malvira/go,vsekhar/elastic-go,linux-on-ibm-z/go,nawawi/go,sndnvaps/go,Samurais/go,cloudflare/go,linux-on-ibm-z/go,theif519/go,theif519/go,vanloswang/go,deft-code/go,CAFxX/go,suncycheng/go,binarycrusader/go,vsekhar/elastic-go,CAFxX/go,Endika/go,cloudflare/go,rachtsingh/gogojuice,ganboing/go-esx,gdey/go,ImJasonH/go,codestation/go,fjballest/golang,christopher-henderson/Go,codestation/go,golang/go,derekmarcotte/go,kim-racktop/go,suncycheng/go,Jordanzuo/go,goodlang/good,4ad/go,kim-racktop/go,nawawi/go,kim-racktop/go,fjballest/golang,suncycheng/go,polyverse-security/go,derekmarcotte/go,roth1002/go,rachtsingh/gogojuice,miolini/go,nawawi/go,Samurais/go,theif519/go,vsekhar/elastic-go,akutz/go,rachtsingh/gogojuice,miolini/go,binarycrusader/go,sndnvaps/go,linux-on-ibm-z/go,momchil-velikov/go,malvira/go,kim-racktop/go,vsekhar/elastic-go,derekmarcotte/go,vanloswang/go,polyverse-security/go,cloudflare/go,Cofyc/go,deft-code/go,4ad/go,miolini/go,vanloswang/go,golang/go,roth1002/go,linux-on-ibm-z/go,linux-on-ibm-z/go,suncycheng/go,josharian/go,derekmarcotte/go,Cofyc/go,goodlang/good,Samurais/go,derekmarcotte/go,momchil-velikov/go,akutz/go,CAFxX/go,vanloswang/go,sndnvaps/go,vsekhar/elastic-go,4ad/go,josharian/go,Jordanzuo/go,rachtsingh/gogojuice,vsekhar/elastic-go,Endika/go,vsekhar/elastic-go,cloudflare/go,mwhudson/go,mwhudson/go,deft-code/go,kim-racktop/go,roth1002/go,vsekhar/elastic-go,rachtsingh/gogojuice,rachtsingh/gogojuice,Cofyc/go,Endika/go,akutz/go,golang/go,polyverse-security/go,Cofyc/go,codestation/go,binarycrusader/go,fjballest/golang,odeke-em/go,rachtsingh/gogojuice,vanloswang/go,momchil-velikov/go,Samurais/go,akutz/go,mwhudson/go,ImJasonH/go,suncycheng/go,josharian/go,momchil-velikov/go,momchil-velikov/go,fjballest/golang,golang/go,goodlang/good,fjballest/golang,theif519/go,nawawi/go,linux-on-ibm-z/go,odeke-em/go,cyberroadie/go,theif519/go,goodlang/good,ganboing/go-esx,gdey/go,ImJasonH/go,fjballest/golang