Add CodeQL badge

Author: vanbroup

README.md

@@ -2,6 +2,7 @@
 
 [![Build & Test](https://github.com/digitorus/timestamp/workflows/Build%20&%20Test/badge.svg)](https://github.com/digitorus/timestamp/actions?query=workflow%3Abuild-and-test)
 [![golangci-lint](https://github.com/digitorus/timestamp/workflows/golangci-lint/badge.svg)](https://github.com/digitorus/timestamp/actions?query=workflow%3Agolangci-lint)
+[![CodeQL](https://github.com/digitorus/timestamp/workflows/CodeQL/badge.svg)](https://github.com/digitorus/timestamp/actions?query=workflow%3Acodeql)
 [![Go Report Card](https://goreportcard.com/badge/github.com/digitorus/timestamp)](https://goreportcard.com/report/github.com/digitorus/timestamp)
 [![Coverage Status](https://codecov.io/gh/digitorus/timestamp/branch/master/graph/badge.svg)](https://codecov.io/gh/digitorus/timestamp)
 [![Go Reference](https://pkg.go.dev/badge/github.com/digitorus/timestamp.svg)](https://pkg.go.dev/github.com/digitorus/timestamp)