fix link to v3 docs (#558)

Author: jjlin

README.md

@@ -3,7 +3,7 @@ go-restful
 package for building REST-style Web Services using Google Go
 
 [![Go Report Card](https://goreportcard.com/badge/github.com/emicklei/go-restful)](https://goreportcard.com/report/github.com/emicklei/go-restful)
-[![GoDoc](https://godoc.org/github.com/emicklei/go-restful?status.svg)](https://pkg.go.dev/github.com/emicklei/go-restful)
+[![Go Reference](https://pkg.go.dev/badge/github.com/emicklei/go-restful.svg)](https://pkg.go.dev/github.com/emicklei/go-restful/v3)
 [![codecov](https://codecov.io/gh/emicklei/go-restful/branch/master/graph/badge.svg)](https://codecov.io/gh/emicklei/go-restful)
 
 - [Code examples use v3](https://github.com/emicklei/go-restful/tree/v3/examples)