Add output to build task

Rakefile

 task 'build' do
   scss = File.read('./web/assets/style.scss')
   css = SassC::Engine.new(scss, style: :compressed).render
+  puts 'Writing web/public/style.css'
   File.write('./web/public/style.css', css)
   js = File.read('./web/assets/script.js')
+  puts 'Writing web/public/script.js'
   File.write('./web/public/script.js', js)
 end