Clarify build instructions
Clarify build instructions

Closes gh-272

bclozel/initializr,gwidgets/gwt-project-generator,nevenc-pivotal/initializr,spring-io/initializr,nevenc-pivotal/initializr,nevenc-pivotal/initializr,bclozel/initializr,bclozel/initializr,gwidgets/gwt-project-generator,gwidgets/gwt-project-generator,snicoll/initializr,nevenc-pivotal/initializr,spring-io/initializr,nevenc-pivotal/initializr,Arsene07/forge,Arsene07/forge,spring-io/initializr,gwidgets/gwt-project-generator,bclozel/initializr,bclozel/initializr,Arsene07/forge,Arsene07/forge,snicoll/initializr,snicoll/initializr,Arsene07/forge