Adding pom.xml instructions

+ for how generate ANTLR  source files

ethereumj-core/pom.xml

@@ -9,9 +9,11 @@
 	<url>http://www.ethereumj.org</url>
 
 <!--
-* To deploy the classes in one jar and dependencies to another dir
-mvn clean package -Dmaven.test.skip=true
+ * To deploy the classes in one jar and dependencies to another dir
+ mvn clean package -Dmaven.test.skip=true
 
+ * To generate source for ANTLR parser/lexer
+ mvn antlr4:antlr4
 -->
 
 	<properties>