update README and examples.

Author: skoji

README.md

@@ -15,7 +15,6 @@ a generic EPUB parser/generator library.
 
 * GEPUB::Book provides functionality to create EPUB file, and parsing EPUB files
 * Handle every metadata in EPUB2/EPUB3.
-* GEPUB::Builder provides an easy way to create EPUB3 files
 
 * See [issues](https://github.com/skoji/gepub/issues/) for known problems.
 

examples/builder_example.rb examples/deprecated_builder_example.rb

@@ -1,4 +1,6 @@
 # -*- coding: utf-8 -*-
+# We will continue to support GEPUB::Builder works fine on version 1.x, but Builder will not be updated any more. For example, landmarks are not supported with Builder.
+
     require 'rubygems'
     require 'gepub'
     workdir = 'epub/example/'