add links for pdf version, hardcopy and sources

Author: shenzhun

README.md

@@ -3,4 +3,5 @@ data-structures-and-algorithms-in-python
 
 "Data Structures and Algorithms in Python" is designed to provide an introduction to data structures and algorithms, including their design, analysis, and implementation. The authors take advantage of the beauty and simplicity of Python to present executable source code that is clear and concise. Furthermore, a consistent object-oriented viewpoint is retained throughout the book, including the use of inheritance, both to maximize code reuse and to draw attention to the clear similarities and differences of various abstract data types and algorithmic approaches.
 
-Use this link (http://as.wiley.com/WileyCDA/WileyTitle/productCd-EHEP002510.html) to find more information
+pdf version can be found by IT-ebook (http://it-ebooks.info/book/2467/). Hardcopy can be found on http://www.amazon.com/dp/1118290275. Use this link (http://as.wiley.com/WileyCDA/WileyTitle/productCd-EHEP002510.html) to find more information
+