doc: discuss copyright changes in contribute.html
doc: discuss copyright changes in contribute.html

Fixes #12542.

Change-Id: Icd0fa84d891d6b1feab9b4d4dd319cdf1e6d6c48
Reviewed-on: https://go-review.googlesource.com/18336
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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