Update free-programming-books-subjects.md (#6252)

Added How to manage remote servers with ansible book.

books/free-programming-books-subjects.md

@@ -504,6 +504,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [HoloLens Succinctly](https://www.syncfusion.com/ebooks/hololens_succinctly) - Lars Klint
 * [How Computers Work](http://www.fastchip.net/howcomputerswork/p1.html) - R. Young
 * [How to Become a Programmer](http://softwarebyrob.wpengine.netdna-cdn.com/assets/Software_by_Rob%20_How_to_Become_a%20_Programmer_1.0.pdf) (PDF)
+* [How To Manage Remote Servers with Ansible](https://www.digitalocean.com/community/books/how-to-manage-remote-servers-with-ansible-ebook) - Erika Heidi (PDF, EPUB)
 * [How to Think Like a Computer Scientist](http://openbookproject.net/thinkcs/) - Peter Wentworth, Jeffrey Elkner, Allen B. Downey, and Chris Meyers
 * [Image Processing in C: Analyzing and Enhancing Digital Images](http://homepages.inf.ed.ac.uk/rbf/BOOKS/PHILLIPS/) - Dwayne Phillips
 * [Information Technology and the Networked Economy](http://florida.theorangegrove.org/og/file/49843a6a-9a9d-4bad-b4d4-d053f9cdf73e/1/InfoTechNetworkedEconomy.pdf) (PDF)