Add Javadoc to ParametersTransformer

Author: abelsromero

spring-cloud-app-broker-core/src/main/java/org/springframework/cloud/appbroker/extensions/parameters/ParametersTransformer.java

@@ -20,6 +20,10 @@
 
 import reactor.core.publisher.Mono;
 
+/**
+ * Mutates the provided backing type.
+ * Returned value is effectively ignored.
+ */
 @FunctionalInterface
 public interface ParametersTransformer<T> {