Include the name of the template file instead of just rake

lib/ffi/tools/generator.rb

@@ -79,7 +79,7 @@ def initialize(ffi_name, rb_name, options = {})
       end
 
       open @rb_name, 'w' do |f|
-        f.puts "# This file is generated by rake. Do not edit."
+        f.puts "# This file is generated from `#{@ffi_name}'. Do not edit."
         f.puts
         f.puts new_file
       end