Adding documentation regarding lazy_load_hooks

activesupport/lib/active_support/lazy_load_hooks.rb

@@ -1,3 +1,22 @@
+# lazy_load_hooks allows rails to lazily load a lot of components and thus making the app boot faster. Because of 
+# this feature now there is no need to require <tt>ActiveRecord::Base</tt> at boot time purely to apply configuration. Instead
+# a hook is registered that applies configuration once <tt>ActiveRecord::Base</tt> is loaded. Here <tt>ActiveRecord::Base</tt> is used
+# as example but this feature can be applied elsewhere too.
+#
+# Here is an example where +on_load+ method is called to register a hook.
+#
+#  initializer "active_record.initialize_timezone" do
+#    ActiveSupport.on_load(:active_record) do
+#      self.time_zone_aware_attributes = true
+#      self.default_timezone = :utc
+#    end
+#  end
+#
+# When the entirety of +activerecord/lib/active_record/base.rb+ has been evaluated then +run_load_hooks+ is invoked. 
+# The very last line of +activerecord/lib/active_record/base.rb+ is:
+#
+#  ActiveSupport.run_load_hooks(:active_record, ActiveRecord::Base)
+#
 module ActiveSupport
   @load_hooks = Hash.new {|h,k| h[k] = [] }
   @loaded = {}
@@ -24,4 +43,4 @@ module ActiveSupport
       execute_hook(base, options, hook)
     end
   end
-end
+end