Add documention for Sidetiq::Schedulable.

lib/sidetiq/schedulable.rb

@@ -1,7 +1,18 @@
 module Sidetiq
+  # Public: Mixin for Sidekiq::Worker classes.
+  #
+  # Examples
+  #
+  #   class MyWorker
+  #       include Sidekiq::Worker
+  #       include Sidetiq::Schedulable
+  #
+  #       # Daily at midnight
+  #       tiq { daily }
+  #     end
   module Schedulable
     module ClassMethods
-      def tiq(&block)
+      def tiq(&block) # :nodoc:
         clock = Sidetiq::Clock.instance
         clock.synchronize do
           clock.schedule_for(self).instance_eval(&block)
@@ -9,7 +20,7 @@ module Sidetiq
       end
     end
 
-    def self.included(klass)
+    def self.included(klass) # :nodoc:
       klass.extend(Sidetiq::Schedulable::ClassMethods)
     end
   end