Added Distributed Systems 3rd edition (#6219)

Added Distributed Systems 3rd edition to the Cloud Computing section.

books/free-programming-books-subjects.md

@@ -155,6 +155,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [Cloud Computing for Science and Engineering](https://cloud4scieng.org/chapters/) - Ian Foster, Dennis B. Gannon (:construction: *in process*)
 * [Cloud Design Patterns](https://docs.microsoft.com/en-us/azure/architecture/patterns/)
 * [Designing Distributed Systems](https://azure.microsoft.com/en-us/resources/designing-distributed-systems/) *(account required)*
+* [Distributed Systems 3rd edition](https://www.distributed-systems.net/index.php/books/ds3/) Maarten van Steen, Andrew S. Tanenbaum *(email address required)*
 * [How to optimize storage costs using Amazon S3](https://aws.amazon.com/s3/cloud-storage-cost-optimization-ebook/) - AWS (PDF)
 * [Kubernetes Hardening Guidance](https://media.defense.gov/2021/Aug/03/2002820425/-1/-1/1/CTR_KUBERNETESHARDENINGGUIDANCE.PDF) - NSA, CISA (PDF)
 * [Learn Azure in a Month of Lunches](https://azure.microsoft.com/mediahandler/files/resourcefiles/learn-azure-in-a-month-of-lunches/Learn_Azure_in_a_Month_of_Lunches.pdf) - Iain Foulds (PDF)