go_repository: document build_file_proto_mode attr (#1011)
go_repository: document build_file_proto_mode attr (#1011)

[skip ci]
[ci skip]
bazelbuild/rules_go,Xjs/rules_go,Xjs/rules_go,Xjs/rules_go,Xjs/rules_go,bazelbuild/rules_go,Xjs/rules_go,bazelbuild/rules_go,bazelbuild/rules_go,bazelbuild/rules_go