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: I8b1e4a877bd83fe6891688a44d27a6c7902c8979
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/624155
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>

Author: ianlancetaylor

README.md

@@ -2,20 +2,17 @@
 
 [![Go Reference](https://pkg.go.dev/badge/golang.org/x/crypto.svg)](https://pkg.go.dev/golang.org/x/crypto)
 
-This repository holds supplementary Go cryptography libraries.
-
-## Download/Install
-
-The easiest way to install is to run `go get -u golang.org/x/crypto/...`. You
-can also manually git clone the repository to `$GOPATH/src/golang.org/x/crypto`.
+This repository holds supplementary Go cryptography packages.
 
 ## 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/crypto.
 
 The main issue tracker for the crypto repository is located at
-https://github.com/golang/go/issues. Prefix your issue with "x/crypto:" in the
+https://go.dev/issues. Prefix your issue with "x/crypto:" in the
 subject line, so it is easy to find.
 
 Note that contributions to the cryptography package receive additional scrutiny