Added custom Dashboard tutorial to menu.md
Added custom Dashboard tutorial to menu.md

Added custom Dashboard tutorial to menu.md based on loostro's
explanation

symfony2admingenerator/AdmingeneratorGeneratorBundle,Restless-ET/AdmingeneratorGeneratorBundle,Restless-ET/AdmingeneratorGeneratorBundle,Restless-ET/AdmingeneratorGeneratorBundle,symfony2admingenerator/AdmingeneratorGeneratorBundle