[FLINK-9483] 'Building Flink' doc doesn't highlight quick build command

This closes #6109

docs/start/building.md

@@ -50,7 +50,11 @@ mvn clean install -DskipTests
 
 This instructs [Maven](http://maven.apache.org) (`mvn`) to first remove all existing builds (`clean`) and then create a new Flink binary (`install`).
 
-To speed up the build you can skip tests, checkstyle, and JavaDocs: `mvn clean install -DskipTests -Dmaven.javadoc.skip=true -Dcheckstyle.skip=true`.
+To speed up the build you can skip tests, QA plugins, and JavaDocs:
+
+{% highlight bash %}
+mvn clean install -DskipTests -Dfast
+{% endhighlight %}
 
 The default build adds a Flink-specific JAR for Hadoop 2, to allow using Flink with HDFS and YARN.