chore(readme): add release badge (swaggo#394)

README.md

@@ -9,6 +9,7 @@
 [![Go Doc](https://godoc.org/github.com/swaggo/swagg?status.svg)](https://godoc.org/github.com/swaggo/swag)
 [![Backers on Open Collective](https://opencollective.com/swag/backers/badge.svg)](#backers) 
 [![Sponsors on Open Collective](https://opencollective.com/swag/sponsors/badge.svg)](#sponsors) [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bgithub.com%2Fswaggo%2Fswag.svg?type=shield)](https://app.fossa.io/projects/git%2Bgithub.com%2Fswaggo%2Fswag?ref=badge_shield)
+[![Release](https://img.shields.io/github/release/swaggo/swag.svg?style=flat-square)](https://github.com/swaggo/swag/releases)
 
 
 Swag converts Go annotations to Swagger Documentation 2.0. We've created a variety of plugins for popular [Go web frameworks](#supported-web-frameworks). This allows you to quickly integrate with an existing Go project (using Swagger UI).