Added a few Linux books

free-programming-books.md

@@ -1053,9 +1053,13 @@ See also [TeX](#tex)
 ###Linux
 * [Ad Hoc Data Analysis From The Unix Command Line](http://en.wikibooks.org/wiki/Ad_Hoc_Data_Analysis_From_The_Unix_Command_Line)
 * [Advanced Linux Programming](http://www.advancedlinuxprogramming.com/)
+* [Automated Linux From Scratch](http://www.linuxfromscratch.org/alfs/download.html)
+* [Beyond Linux From Scratch](http://www.linuxfromscratch.org/blfs/downloads/stable/BLFS-BOOK-7.5-nochunks.html)
+* [Cross Linux From Scratch](http://trac.cross-lfs.org/wiki/download#CurrentStable)
 * [Getting Started with Ubuntu](http://ubuntu-manual.org/)
 * [GNU Autoconf, Automake and Libtool](http://sources.redhat.com/autobook/download.html)
 * [GTK+/Gnome Application Development](http://www.linuxtopia.org/online_books/gui_toolkit_guides/gtk+_gnome_application_development/index.html)
+* [Hardened Linux From Scratch](http://www.linuxfromscratch.org/hlfs/download.html)
 * [Learning Debian GNU/Linux](http://oreilly.com/openbook/debian/book/index.html)
 * [Linux Administrator's Security Guide](http://www.linuxtopia.org/online_books/linux_administrators_security_guide/index.html)
 * [Linux Advanced Routing & Traffic Control HOWTO](http://lartc.org/)