Add descriptions to rake tasks

This makes them listable with `rake -T`

Rakefile

@@ -1,14 +1,17 @@
 task :default => :build
 
+desc 'Build the site from source'
 task :build do
   system("jekyll build")
 end
 
+desc 'Deploy the site to the exciting.io server'
 task :deploy => :build do
   system("rsync -avz --delete _site/ exciting.io:exciting.io")
   Rake::Task[:fix_permissions].invoke
 end
 
+desc 'Ensure that the deployed files have the right permissions'
 task :fix_permissions do
   system("ssh exciting.io 'chmod og+r -R exciting.io'")
 end