cmd/go: document GOBIN and 'go install' locations

* In doc/install-source.html, clarify the meaning of $GOBIN and
  describe where executables from the Go distribution are
  installed. Also describe $GOPATH, since it provides a default value
  for $GOBIN and may conflict with $GOROOT.
* Add more detail to 'go help install' as well.

Fixes #31576

Change-Id: Ib8a8c21677c3aa0ebef97a3b587b6f8fe338b80e
Reviewed-on: https://go-review.googlesource.com/c/go/+/182341
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 9c03f0818d..ed5a149da3 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/src/cmd/go/internal/work/build.go
@@ -404,6 +404,15 @@ var CmdInstall = &base.Command{
 	Long: `
 Install compiles and installs the packages named by the import paths.
 
+Executables are installed in the directory named by the GOBIN environment
+variable, which defaults to $GOPATH/bin or $HOME/go/bin if the GOPATH
+environment variable is not set. Executables in $GOROOT
+are installed in $GOROOT/bin or $GOTOOLDIR instead of $GOBIN.
+
+When module-aware mode is disabled, other 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.
+
 The -i flag installs the dependencies of the named packages as well.
 
 For more about the build flags, see 'go help build'.