compress/gzip: document Reader.Read
compress/gzip: document Reader.Read

Fixes #17374.

Change-Id: Ic89c35aaa31f35a8a4e3ffa09f49b68f08127625
Reviewed-on: https://go-review.googlesource.com/30718
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>

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