Adds site reliability engineering workbook (#4731)

* Adds The Site Reliability Workbook

* Sorts new book

* Adds back empty line

free-programming-books.md

@@ -829,6 +829,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Software Architecture Patterns](http://www.oreilly.com/programming/free/software-architecture-patterns.csp) (email address *requested*, not required)
 * [Software Engineering for Internet Applications](http://philip.greenspun.com/seia/)
 * [Test Driven Development, Extensive Tutorial](https://github.com/grzesiek-galezowski/tdd-ebook) - Grzegorz Gałęzowski
+* [The Site Reliability Workbook](https://landing.google.com/sre/workbook/toc/) - Betsy Beyer, Niall Richard Murphy, David K. Rensin, Kent Kawahara and Stephen Thorne
 * [Web API Design](https://pages.apigee.com/rs/apigee/images/api-design-ebook-2012-03.pdf) - Brian Mulloy (PDF)
 * [Working with Web APIs](https://launchschool.com/books/working_with_apis) - Launch School
 * [Your API Is Bad](https://leanpub.com/yourapiisbad/read) - Paddy Foran