Fix README and require annotate in InstallGenerator (#494)

* Fix InstallGenerator to require annotate
* Fix README

Author: yhirano55

README.rdoc

@@ -55,11 +55,11 @@ Also, if you pass the -r option, it'll annotate routes.rb with the output of
 
 Into Gemfile from rubygems.org:
 
-    gem 'annotate'
+    gem 'annotate', require: false
 
 Into Gemfile from Github:
 
-    gem 'annotate', git: 'https://github.com/ctran/annotate_models.git'
+    gem 'annotate', github: 'ctran/annotate_models', require: false
 
 Into environment gems from rubygems.org:
 

lib/generators/annotate/install_generator.rb

@@ -1,8 +1,10 @@
+require 'annotate'
+
 module Annotate
   module Generators
     class InstallGenerator < Rails::Generators::Base
       desc 'Copy annotate_models rakefiles for automatic annotation'
-      source_root File.expand_path('../templates', __FILE__)
+      source_root File.expand_path('templates', __dir__)
 
       # copy rake tasks
       def copy_tasks