RPi OS development tutorial added (#2892)

* RPi OS development tutorial added

* moved to free-programming-interactive-tutorials-en.md

* emty line added

free-programming-interactive-tutorials-en.md

@@ -16,6 +16,7 @@
 * [Javascript](#javascript)
   * [Angular.js](#angularjs)
 * [Language Agnostic](#language-agnostic)
+  * [Operating Systems](#operating-systems)
 * [Lisp](#lisp)
 * [MATLAB](#matlab)
 * [Node](#node)
@@ -140,6 +141,11 @@
 * [The Fullstack Tutorial for GraphQL](https://www.howtographql.com)
 
 
+#### Operating systems
+
+* [Learning operating system development using Linux kernel and Raspberry Pi](https://github.com/s-matyukevich/raspberry-pi-os) - Sergey Matyukevich (:construction: *in process*)
+
+
 ### Lisp
 
 * [Lisp Koans](https://github.com/google/lisp-koans)