chore: verify google code format

Author: oliemansm

CONTRIBUTING.md

@@ -0,0 +1,46 @@
+# How to contribute
+
+We're really glad you're reading this, because we need more volunteer developers
+to help with this project!
+
+We can use all the help we can get on all our [GraphQL Java Kickstart](https://github.com/graphql-java-kickstart)
+projects. This work ranges from adding new features, fixing bugs, and answering questions to writing documentation. 
+
+## Answering questions and writing documentation
+
+A lot of the questions asked on Spectrum or Github are caused by a lack of documentation.
+We should strive from now on to answer questions by adding content to 
+our [documentation](https://github.com/graphql-java-kickstart/documentation) and referring
+them to the newly created content.
+
+Continuous integration will make sure that the changes are automatically deployed to 
+https://www.graphql-java-kickstart.com.
+
+## Submitting changes
+
+Please send a Pull Request with a clear list of what you've done using the
+[Github flow](https://guides.github.com/introduction/flow/). We can always use more
+test coverage, so we'd love to see that in the pull requests too. And make sure to
+follow our coding conventions (below) and make sure all your commits are atomic 
+(one feature per commit).
+
+## Coding conventions
+
+We use Google Style guides for our projects. See the 
+[Java Style Guide](https://google.github.io/styleguide/javaguide.html) for a detailed
+description. You can download the 
+[IntelliJ Java Google Style](https://github.com/google/styleguide/blob/gh-pages/intellij-java-google-style.xml)
+to import in these settings in IntelliJ.
+
+These conventions are checked during the build phase. If the build fails because
+the code is not using the correct style you can fix this easily by running a gradle task
+```bash
+./gradlew googleJavaFormat
+```
+
+### SonarLint
+
+It would also be very helpful to install the SonarLint plugin in your IDE and fix any
+relevant SonarLint issues before pushing a PR. We're aware that the current state
+of the code raises a lot of SonarLint issues out of the box, but any help in reducing
+that is appreciated. More importantly we don't increase that technical debt.

build.gradle

@@ -25,6 +25,7 @@ plugins {
     id "org.sonarqube" version "3.2.0"
     id "jacoco"
     id 'io.codearte.nexus-staging' version '0.30.0'
+    id 'com.github.sherter.google-java-format' version '0.9' apply false
 }
 
 sonarqube {
@@ -48,6 +49,7 @@ subprojects {
     }
     apply plugin: 'maven-publish'
     apply plugin: 'signing'
+    apply plugin: 'com.github.sherter.google-java-format'
 
     group "$PROJECT_GROUP"
 
@@ -114,6 +116,8 @@ subprojects {
         }
 
         compileJava.dependsOn(processResources)
+
+        compileJava.mustRunAfter verifyGoogleJavaFormat
     }
 
     if (!it.name.startsWith('example')) {