Add Android and Linux books

free-programming-books.md

@@ -424,6 +424,7 @@
 * [Styling Android](http://www.stylingandroid.com/)
 * [TechnoTalkative Android](http://www.technotalkative.com/android/)
 * [Android Programming Guide for Beginners](http://eduonix.com/offers/Android_ebook_free_offer.html) (PDF - need email confirmation)
+* [Android 4 App Development Essentials](http://www.techotopia.com/index.php/Android_4_App_Development_Essentials)
 
 
 ###APL
@@ -819,6 +820,8 @@ See also [TeX](#tex)
 * [What Every Programmer Should Know About Memory](http://www.akkadia.org/drepper/cpumemory.pdf) (PDF)
 * [Learning Debian GNU/Linux](http://oreilly.com/openbook/debian/book/index.html)
 * [Upstart Intro, Cookbook and Best Practises](http://upstart.ubuntu.com/cookbook/)
+* [Red Hat Enterprise Linux 6 Essentials](http://www.techotopia.com/index.php/Red_Hat_Enterprise_Linux_6_Essentials)
+
 
 ###Lisp
 * [Common Lisp the Language, 2nd Edition](http://www.cs.cmu.edu/Groups/AI/html/cltl/mirrors.html)