cmd/go: document GODEBUG=installgoroot=all

At the moment the only documentation is the release notes,
but everything mentioned in the release notes should have
proper documentation separate from them.

Change-Id: I9885962f6c6d947039b0be59b608385781479271
Reviewed-on: https://go-review.googlesource.com/c/go/+/462196
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 4c72ab6d56..84afcab7a0 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -746,9 +746,15 @@
 // If module-aware mode is enabled, "go install" runs in the context of the main
 // module.
 //
-// When module-aware mode is disabled, other packages are installed in the
+// When module-aware mode is disabled, non-main packages are installed in the
 // directory $GOPATH/pkg/$GOOS_$GOARCH. When module-aware mode is enabled,
-// other packages are built and cached but not installed.
+// non-main packages are built and cached but not installed.
+//
+// Before Go 1.20, the standard library was installed to
+// $GOROOT/pkg/$GOOS_$GOARCH.
+// Starting in Go 1.20, the standard library is built and cached but not installed.
+// Setting GODEBUG=installgoroot=all restores the use of
+// $GOROOT/pkg/$GOOS_$GOARCH.
 //
 // For more about the build flags, see 'go help build'.
 // For more about specifying packages, see 'go help packages'.