cmd/go: doc: no official explanation about GOCACHE=off ?

[hirochachacha]

As far as I can see, I could not find the documentation about that.

[agnivade]

@ianlancetaylor - How about adding something like this

You can set the variable to "off" if you want to bypass the cache

at the end of https://github.com/golang/go/blob/master/src/cmd/go/internal/help/helpdoc.go#L659, which is the output of go help cache.

[ianlancetaylor]

@agnivade Sure, maybe at the end of the first paragraph that discusses GOCACHE.

[gopherbot]

Change https://golang.org/cl/119695 mentions this issue: cmd/go/internal: add a note about GOCACHE=off