extras/courses: Add Introduction to Computational Thinking by MIT

As noted here ossu#912 adding this course to The Math section

Author: Dody2

extras/courses.md

@@ -35,6 +35,7 @@ Courses | Duration | Effort
 [Advanced Precalculus](https://www.futurelearn.com/courses/advanced-precalculus) | 4 weeks | 5 hours/week
 [Introduction to Probability and Data](https://www.coursera.org/learn/probability-intro)| - | -
 [Linear Algebra (Strang)](https://ocw.mit.edu/courses/mathematics/18-06-linear-algebra-spring-2010/index.htm) | - | -
+[Introduction to Computational Thinking](https://computationalthinking.mit.edu/Spring21/#introduction_to_computational_thinking) | - | -
 [Multivariable Calculus](https://ocw.mit.edu/courses/mathematics/18-02sc-multivariable-calculus-fall-2010/index.htm) | 13 weeks | 12 hours/week
 [Introduction to Probability - The Science of Uncertainty](https://www.edx.org/course/introduction-probability-science-mitx-6-041x-2) | 18 weeks | 12 hours/week | [Multivariable Calculus](https://ocw.mit.edu/courses/mathematics/18-02sc-multivariable-calculus-fall-2010/index.htm)