Make the question more clear (for composition)

When the generator is being composed, people using the other generator might not be aware of its presence, so it's unclear what "Choose your style of DSL" refers to.

Ref. yeoman/generator-webapp#545.
Ref. yeoman/generator-webapp#538.

generators/app/index.js

@@ -6,7 +6,7 @@ module.exports = generators.Base.extend({
     generators.Base.apply(this, arguments);
 
     this.option('ui', {
-      desc: 'Choose your style of DSL (bdd, tdd)',
+      desc: 'Choose your style of test DSL for Mocha (bdd, tdd)',
       type: String
     });