docs(build): make the CI build badge clickable (#1828)

README.md

@@ -1,4 +1,4 @@
-![Build Status](https://github.com/stryker-mutator/stryker/workflows/CI/badge.svg)
+[![Build Status](https://github.com/stryker-mutator/stryker/workflows/CI/badge.svg)](https://github.com/stryker-mutator/stryker/actions?query=workflow%3ACI+branch%3Amaster)
 [![NPM](https://img.shields.io/npm/dm/@stryker-mutator/core.svg)](https://www.npmjs.com/package/@stryker-mutator/core)
 [![Node version](https://img.shields.io/node/v/@stryker-mutator/core.svg)](https://img.shields.io/node/v/@stryker-mutator/core.svg)
 [![Gitter](https://badges.gitter.im/stryker-mutator/stryker.svg)](https://gitter.im/stryker-mutator/stryker?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)