Added Conquering the Command Line

free-programming-books.md

@@ -1427,6 +1427,7 @@ See also [LaTeX](#latex)
 
 ###Unix
 * [A User's Guide for GNU AWK](http://www.math.utah.edu/docs/info/gawk_toc.html)
+* [Conquering the Command Line](http://www.conqueringthecommandline.com/)
 
 
 ###Vim