Update Javadoc for AbstractListenerWriteProcessor.write()

Co-authored-by: Rossen Stoyanchev <rstoyanchev@pivotal.io>

spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java

@@ -213,6 +213,9 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 	 * @param data the item to write
 	 * @return whether the current data item was written and another one
 	 * requested ({@code true}), or otherwise if more writes are required.
+	 * @return {@code true} if the current data item was written completely and
+	 * a new item requested, or {@code false} if it was written partially and
+	 * we'll need more write callbacks before it is fully written
 	 */
 	protected abstract boolean write(T data) throws IOException;