cmd/go: missing documentation for GO111MODULE in go help environment

[FotiadisM]

What version of Go are you using (go version)?

$ go version go1.15.6 linux/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/fotiadis/.cache/go-build"
GOENV="/home/fotiadis/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/fotiadis/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/fotiadis/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build592834114=/tmp/go-build -gno-record-gcc-switches"

What did you do?

go help environment

What did you expect to see?

Documentation about the module-aware mode

What did you see instead?

No info

[gopherbot]

Change https://golang.org/cl/280812 mentions this issue: help: add doc for GO111MODULE.

[gopherbot]

Change https://golang.org/cl/282615 mentions this issue: cmd/go: revise 'go help' documentation for modules