Added a link to the linked maven plugin

Author: EtienneSF

README.md

@@ -1,2 +1,4 @@
 # graphql-gradle-plugin-project
 graphql-gradle-plugin is a Gradle Plugin for GraphQL, based on graphql-java. It accelerates the development for both the client and the server, by generating the Java code. It allows a quicker development when in contract-first approach, by avoiding to code the boilerplate code. 
+
+The plugin is currently under development. But it should be quite quick, as is is a port on Gradle of the [graphql-java-generator maven plugin](https://github.com/graphql-java-generator/graphql-maven-plugin-project).