docs: add GitHub Actions CI badge

Author: BlasiusSecundus

README.md

@@ -1,5 +1,6 @@
 # GraphQL and Graph*i*QL Spring Framework Boot Starters
 [![Build Status](https://travis-ci.org/graphql-java-kickstart/graphql-spring-boot.svg?branch=master)](https://travis-ci.org/graphql-java-kickstart/graphql-spring-boot)
+[![GitHub CI Workflow](https://github.com/graphql-java-kickstart/graphql-spring-boot/workflows/CI/badge.svg)](https://github.com/graphql-java-kickstart/graphql-spring-boot/actions?query=workflow%3ACI+branch%3Amaster)
 [![Maven Central](https://img.shields.io/maven-central/v/com.graphql-java-kickstart/graphql-spring-boot-starter.svg)](https://maven-badges.herokuapp.com/maven-central/com.graphql-java-kickstart/graphql-spring-boot-starter)
 [![Chat on Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/graphql-java-kickstart/Lobby)