This adds descriptions to the rake tasks

This adds the descriptions to the rake tasks so you can now
do rake -T to see the option you have to run.

Change-Id: I5c2546481f753576e8b01f7a2f2815397af68b75
Closes-Bug: 1397722

Rakefile

@@ -2,27 +2,33 @@ task default: ["test"]
 
 task :test => [:lint, :style, :unit]
 
+desc "Bundler preparation"
 task :bundler_prep do
   mkdir_p '.bundle'
   sh %{bundle install --path=.bundle --jobs 1 --retry 3 --verbose}
 end
 
+desc "Bershelf preparation"
 task :berks_prep => :bundler_prep do
   sh %{bundle exec berks vendor}
 end
 
+desc "Foodcritic linting"
 task :lint => :bundler_prep do
   sh %{bundle exec foodcritic --epic-fail any --tags ~FC003 --tags ~FC023 .}
 end
 
+desc "Rubocop style checking"
 task :style => :bundler_prep do
   sh %{bundle exec rubocop}
 end
 
+desc "Unit testing"
 task :unit => :berks_prep do
   sh %{bundle exec rspec --format documentation}
 end
 
+desc "Clean up working directory"
 task :clean do
   rm_rf [
     '.bundle',