Add Shape Up by Basecamp's Ryan Singer (#4196)

* Add Shape Up by Basecamp's Ryan Singer

* Update formatting of Shape Up entry

free-programming-books.md

@@ -820,6 +820,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Scrum and XP from the Trenches](http://www.infoq.com/minibooks/scrum-xp-from-the-trenches-2)
 * [Serverless apps: Architecture, patterns, and Azure implementation](https://docs.microsoft.com/en-us/dotnet/standard/serverless-architecture/)
 * [Serverless Design Patterns and Best Practices](https://www.packtpub.com/free-ebooks/serverless-design-patterns-and-best-practices) - Brian Zambrano (Packt account *required*)
+* [Shape Up - Stop Running in Circles and Ship Work that Matters](https://basecamp.com/shapeup) - Ryan Singer (PDF)
 * [Site Reliability Engineering](https://landing.google.com/sre/book/index.html)
 * [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/)