README.md: change godoc.org links to pkg.go.dev

Links to godoc.org are changed to pkg.go.dev.

The README badge alt text is changed to "Go Reference" to match the
updated alt text generated by pkg.go.dev/badge.

Change-Id: I935cbe03477131a4361a8ac7b5ba9fd3e378cbdd
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/276016
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Andrew Gerrand <[email protected]>
Trust: Julie Qiu <[email protected]>

Author: julieqiu

README.md

@@ -1,7 +1,7 @@
 # OAuth2 for Go
 
+[![Go Reference](https://pkg.go.dev/badge/golang.org/x/oauth2.svg)](https://pkg.go.dev/golang.org/x/oauth2)
 [![Build Status](https://travis-ci.org/golang/oauth2.svg?branch=master)](https://travis-ci.org/golang/oauth2)
-[![Go Package Documentation](https://pkg.go.dev/badge/golang.org/x/oauth2.svg)](https://pkg.go.dev/golang.org/x/oauth2)
 
 oauth2 package contains a client implementation for OAuth 2.0 spec.
 
@@ -14,17 +14,17 @@ go get golang.org/x/oauth2
 Or you can manually git clone the repository to
 `$(go env GOPATH)/src/golang.org/x/oauth2`.
 
-See godoc for further documentation and examples.
+See pkg.go.dev for further documentation and examples.
 
-* [godoc.org/golang.org/x/oauth2](https://godoc.org/golang.org/x/oauth2)
-* [godoc.org/golang.org/x/oauth2/google](https://godoc.org/golang.org/x/oauth2/google)
+* [pkg.go.dev/golang.org/x/oauth2](https://pkg.go.dev/golang.org/x/oauth2)
+* [pkg.go.dev/golang.org/x/oauth2/google](https://pkg.go.dev/golang.org/x/oauth2/google)
 
 ## Policy for new packages
 
 We no longer accept new provider-specific packages in this repo if all
 they do is add a single endpoint variable. If you just want to add a
 single endpoint, add it to the
-[godoc.org/golang.org/x/oauth2/endpoints](https://godoc.org/golang.org/x/oauth2/endpoints)
+[pkg.go.dev/golang.org/x/oauth2/endpoints](https://pkg.go.dev/golang.org/x/oauth2/endpoints)
 package.
 
 ## Report Issues / Send Patches