os: document that Rename overwrites existing file
os: document that Rename overwrites existing file

Fixes #13673.

Change-Id: I60d1603ca0dfd2ae136117e0f89cee4b6fc6c3d3
Reviewed-on: https://go-review.googlesource.com/18332
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

codestation/go,CAFxX/go,sndnvaps/go,josharian/go,binarycrusader/go,miolini/go,theif519/go,Endika/go,sndnvaps/go,suncycheng/go,Samurais/go,josharian/go,mwhudson/go,cyberroadie/go,akutz/go,cloudflare/go,derekmarcotte/go,goodlang/good,linux-on-ibm-z/go,josharian/go,goodlang/good,polyverse-security/go,cloudflare/go,cyberroadie/go,4ad/go,golang/go,ganboing/go-esx,ganboing/go-esx,golang/go,CAFxX/go,miolini/go,suncycheng/go,binarycrusader/go,ImJasonH/go,nawawi/go,codestation/go,suncycheng/go,christopher-henderson/Go,vsekhar/elastic-go,cyberroadie/go,goodlang/good,polyverse-security/go,Endika/go,vsekhar/elastic-go,cyberroadie/go,goodlang/good,4ad/go,vanloswang/go,vanloswang/go,polyverse-security/go,akutz/go,ImJasonH/go,golang/go,mwhudson/go,codestation/go,suncycheng/go,mwhudson/go,akutz/go,nawawi/go,goodlang/good,derekmarcotte/go,nawawi/go,vsekhar/elastic-go,linux-on-ibm-z/go,momchil-velikov/go,mwhudson/go,linux-on-ibm-z/go,josharian/go,codestation/go,polyverse-security/go,josharian/go,golang/go,josharian/go,miolini/go,momchil-velikov/go,ganboing/go-esx,4ad/go,codestation/go,miolini/go,akutz/go,binarycrusader/go,Cofyc/go,nawawi/go,vanloswang/go,mwhudson/go,golang/go,theif519/go,nawawi/go,cyberroadie/go,akutz/go,4ad/go,mwhudson/go,CAFxX/go,Samurais/go,cloudflare/go,CAFxX/go,vsekhar/elastic-go,polyverse-security/go,golang/go,goodlang/good,Samurais/go,ImJasonH/go,cloudflare/go,momchil-velikov/go,4ad/go,Endika/go,nawawi/go,miolini/go,Cofyc/go,vanloswang/go,derekmarcotte/go,suncycheng/go,momchil-velikov/go,nawawi/go,suncycheng/go,momchil-velikov/go,sndnvaps/go,derekmarcotte/go,golang/go,theif519/go,cloudflare/go,Samurais/go,momchil-velikov/go,Cofyc/go,vsekhar/elastic-go,Cofyc/go,Endika/go,ganboing/go-esx,vanloswang/go,Cofyc/go,vanloswang/go,theif519/go,ImJasonH/go,ImJasonH/go,polyverse-security/go,akutz/go,CAFxX/go,miolini/go,linux-on-ibm-z/go,cyberroadie/go,akutz/go,binarycrusader/go,miolini/go,linux-on-ibm-z/go,ImJasonH/go,goodlang/good,CAFxX/go,polyverse-security/go,binarycrusader/go,Cofyc/go,derekmarcotte/go,binarycrusader/go,sndnvaps/go,CAFxX/go,Endika/go,sndnvaps/go,vsekhar/elastic-go,josharian/go,ImJasonH/go,ganboing/go-esx,Endika/go,derekmarcotte/go,Cofyc/go,polyverse-security/go,ganboing/go-esx,josharian/go,Samurais/go,ganboing/go-esx,mwhudson/go,4ad/go,cloudflare/go,ImJasonH/go,linux-on-ibm-z/go,momchil-velikov/go,CAFxX/go,miolini/go,vanloswang/go,theif519/go,akutz/go,nawawi/go,mwhudson/go,golang/go,theif519/go,Samurais/go,ganboing/go-esx,4ad/go,momchil-velikov/go,suncycheng/go,codestation/go,sndnvaps/go,sndnvaps/go,codestation/go,Samurais/go,Endika/go,suncycheng/go,Cofyc/go,codestation/go,theif519/go,derekmarcotte/go,linux-on-ibm-z/go,vanloswang/go,binarycrusader/go,vsekhar/elastic-go,theif519/go,goodlang/good,4ad/go,cyberroadie/go,cyberroadie/go,binarycrusader/go,vsekhar/elastic-go,Endika/go,sndnvaps/go,cloudflare/go,derekmarcotte/go,linux-on-ibm-z/go,Samurais/go,cloudflare/go