Add Vulkan tutorial, check_urls=free-programming-books.md (#4859 An error occurred )

* Add Vulkan tutorial C++ #3683
  
An error occurred
 
, check_urls=free-programming-books.md

* Fix url

* Fix space in Vulkan

free-programming-books.md

@@ -57,6 +57,7 @@
 * [Go](#go)
 * [Graphical user interfaces](#graphical-user-interfaces)
 * [Graphics Programming](#graphics-programming)
+  * [Vulkan](#vulkan)
 * [GraphQL](#graphql)
 * [Groovy](#groovy)
   * [Gradle](#gradle)
@@ -293,6 +294,11 @@
 * [WebGL Insights](http://webglinsights.com) - Patrick Cozzi and Contributors
 
 
+#### Vulkan
+
+* [Vulkan Tutorial](https://vulkan-tutorial.com) - Alexander Overvoorde (EPUB, HTML, PDF) (C++)
+
+
 ### Graphical User Interfaces
 
 * [Programming with gtkmm 3](https://developer.gnome.org/gtkmm-tutorial/stable/)