Add git and github book

free-programming-books.md

@@ -1076,6 +1076,7 @@ Original Source: [List of freely available programming books](http://web.archive
 * [Git Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/git) (PDF, Kindle) *(Just fill the fields with any values)*
 * [Git Workflows](http://documentup.com/skwp/git-workflows-book)
 * [GitHub Cheat Sheet](https://github.com/tiimgreen/github-cheat-sheet) - Tim Green (Markdown)
+* [Intoduction to Git and Github](https://launchschool.com/books/git) - Launch School
 * [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) - Jon Forrest