Added book to Parallel Programming section

free-programming-books.md

@@ -213,6 +213,7 @@
 
 ####Parallel Programming
 * [How to Write Parallel Programs](http://www.lindaspaces.com/book/)
+* [High Performance Computing](http://cnx.org/content/col11136/latest) (PDF, ePUB) - Charles Severance & Kevin Dowd
 * [Is Parallel Programming Hard, And, If So, What Can You Do About It?](http://kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.html)
 * [Introduction to Parallel Computing](https://computing.llnl.gov/tutorials/parallel_comp/) - Blaise Barney