Added Functional programming course

Functional programming is a type of programming that should be known by the interested students.

extras/courses.md

@@ -64,7 +64,7 @@ Courses | Duration | Effort
 Courses | Duration | Effort
 :-- | :--: | :--:
 [Principles of Reactive Programming](https://www.coursera.org/course/reactive)| 7 weeks | 5-7 hours/week
-
+[Introduction to Functional Programming](https://www.edx.org/course/introduction-functional-programming-delftx-fp101x-0)| 7 weeks | 4-6 hours/week
 ### Software Testing
 
 ### Math (Calculus)