Updated Algorithms and Data Structures section (#8385)

Added a free course for Data Structures in C++

courses/free-courses-en.md

@@ -141,6 +141,7 @@
 * [Data Structures and Algorithms in Python Full Course for Beginners](https://www.youtube.com/watch?v=pkYVOmU3MgA) - Aakash N S (freeCodeCamp)
 * [Data Structures and Algorithms Specialization](https://www.coursera.org/specializations/data-structures-algorithms) - UC San Diego, HSE University
 * [Data Structures Easy to Advanced Course - Full Tutorial from a Google Engineer](https://www.youtube.com/watch?v=RBSGKlAvoiM) - William Fiset (freeCodeCamp)
+* [Data Structures in C++ - For Beginners](https://www.udemy.com/course/data-structures-for-beginners-c-plusplus) - Pedro Mercado (Udemy)
 * [Dynamic Programming](https://www.youtube.com/playlist?list=PLMCXHnjXnTnto1pZVvH7rbZ9W5neZ7Yhc) - Gaurav Sen
 * [IIT Bombay Foundation of Data Structures (CS213.1x)](https://courses.edx.org/courses/course-v1:IITBombayX+CS213.1x+1T2017/course/)
 * [Intro to Data Structures and Algorithms](https://www.udacity.com/course/data-structures-and-algorithms-in-python--ud513) - Brynn Claypoole, Horatio Thomas (Udacity)