README: don't recommend go get

These days people will just import the packages and the go tool will
do the right thing. We don't need to explain it.

Add a pointer to the git repo, though.

For golang/go#62645

Change-Id: Icbe33e05f96e1b32f6fcc99fb5fb0b2ecb213a08
Reviewed-on: https://go-review.googlesource.com/c/sync/+/623820
Commit-Queue: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

Author: ianlancetaylor

README.md

@@ -5,16 +5,13 @@
 This repository provides Go concurrency primitives in addition to the
 ones provided by the language and "sync" and "sync/atomic" packages.
 
-## Download/Install
-
-The easiest way to install is to run `go get -u golang.org/x/sync`. You can
-also manually git clone the repository to `$GOPATH/src/golang.org/x/sync`.
-
 ## Report Issues / Send Patches
 
 This repository uses Gerrit for code changes. To learn how to submit changes to
-this repository, see https://golang.org/doc/contribute.html.
+this repository, see https://go.dev/doc/contribute.
+
+The git repository is https://go.googlesource.com/sync.
 
 The main issue tracker for the sync repository is located at
-https://github.com/golang/go/issues. Prefix your issue with "x/sync:" in the
+https://go.dev/issues. Prefix your issue with "x/sync:" in the
 subject line, so it is easy to find.