Added "Unix Toolbox"

free-programming-books.md

@@ -1473,7 +1473,7 @@ 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/)
-
+* [Unix Toolbox](http://cb.vu/unixtoolbox.xhtml) - Colin Barschel
 
 ###Vim
 * [A Byte of Vim](http://www.swaroopch.com/notes/Vim)