Merge pull request #1735 from jbranchaud/add-the-red-book

Add Readings In Database Systems (the red book).

free-programming-books.md

@@ -337,6 +337,7 @@ Original Source: [List of freely available programming books](http://web.archive
 * [Big Data Now: Current Perspectives from O'Reilly Radar](http://shop.oreilly.com/product/0636920022640.do)
 * [Database Fundamentals](http://public.dhe.ibm.com/software/dw/db2/express-c/wiki/Database_fundamentals.pdf) (PDF)
 * [Foundations of Databases](http://webdam.inria.fr/Alice/)
+* [Readings in Database Systems, 5th Ed.](http://www.redbook.io)
 * [Temporal Database Management](http://people.cs.aau.dk/~csj/Thesis/) - Christian S. Jensen
 * [The Theory of Relational Databases](http://web.cecs.pdx.edu/~maier/TheoryBook/TRD.html)