Merge pull request #62 from ivpusic/master

Added Git internals

free-programming-books.md

@@ -336,6 +336,7 @@
 
 * [Pro Git](http://git-scm.com/book)
 * [Git From The Bottom Up](http://ftp.newartisans.com/pub/git.from.bottom.up.pdf) (PDF)
+* [Git internals](https://github.com/pluralsight/git-internals-pdf/raw/master/drafts/peepcode-git.pdf) 
 
 
 ###Go