Add license badge (#123)

Author: pellared

README.md

@@ -3,6 +3,7 @@
 [![GitHub Release](https://img.shields.io/github/v/release/golang-templates/seed)](https://github.com/golang-templates/seed/releases)
 [![Go Reference](https://pkg.go.dev/badge/github.com/golang-templates/seed.svg)](https://pkg.go.dev/github.com/golang-templates/seed)
 [![go.mod](https://img.shields.io/github/go-mod/go-version/golang-templates/seed)](go.mod)
+[![LICENSE](https://img.shields.io/github/license/golang-templates/seed)](LICENSE)
 [![Build Status](https://img.shields.io/github/workflow/status/golang-templates/seed/build)](https://github.com/golang-templates/seed/actions?query=workflow%3Abuild+branch%3Amain)
 [![Go Report Card](https://goreportcard.com/badge/github.com/golang-templates/seed)](https://goreportcard.com/report/github.com/golang-templates/seed)
 [![Codecov](https://codecov.io/gh/golang-templates/seed/branch/main/graph/badge.svg)](https://codecov.io/gh/golang-templates/seed)