Added link to opensource Git eBook (#5320)

books/free-programming-books.md

@@ -1466,6 +1466,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [How to Collaborate on Github](https://github.com/eonist/How-to-collaborate-on-github) - André J
 * [Intoduction to Git and Github](https://launchschool.com/books/git) - Launch School
 * [Intoduction to Git and Github - Tutorial](http://cse.unl.edu/~cbourke/gitTutorial.pdf) - Dr. Chris Bourke (PDF)
+* [Introduction to Git and GitHub eBook](https://github.com/bobbyiliev/introduction-to-git-and-github-ebook) - Bobby Iliev (Markdown, PDF)
 * [Learn Git - Learn Version Control with Git](http://www.git-tower.com/learn/git/ebook/command-line/introduction) - Tobias Günther
 * [Pro Git](http://git-scm.com/book/en/v2) - Scott Chacon
 * [Pro Git Reedited](https://leanpub.com/progitreedited/read) - Jon Forrest