Adding details on how to add GraphQL Playground starter

Author: setchy

README.md

@@ -3,6 +3,7 @@
 [![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)
 [![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)
 [![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=graphql-java-kickstart_graphql-spring-boot&metric=alert_status)](https://sonarcloud.io/dashboard?id=graphql-java-kickstart_graphql-spring-boot)
+[![GitHub contributors](https://img.shields.io/github/contributors/graphql-java-kickstart/graphql-spring-boot)](https://img.shields.io/github/contributors/graphql-java-kickstart/graphql-spring-boot)
 
 #### We are looking for contributors!
 
@@ -117,6 +118,9 @@ dependencies {
   // to embed GraphiQL tool
   runtimeOnly 'com.graphql-java-kickstart:graphiql-spring-boot-starter:11.0.0'
 
+  // to embed GraphQL Playground tool
+  runtimeOnly 'com.graphql-java-kickstart:playground-spring-boot-starter:11.0.0'
+
   // to embed Voyager tool
   runtimeOnly 'com.graphql-java-kickstart:voyager-spring-boot-starter:11.0.0'