Add- "Introduction to React" & "Node.js and Express"Course (#5666)

* Add "Data Structures and Algorithms Specialization" link

* Update free-courses-en.md

* Update free-courses-en.md

Author: prajwalkpatil

Diff for: courses/free-courses-en.md

@@ -459,6 +459,7 @@
 * [Beginner's Series to: Node.js](https://youtube.com/playlist?list=PLlrxD0HtieHje-_287YJKhY8tDeSItwtg) - Microsoft Developer (YouTube)
 * [Building a RESTful API with Node.js](https://www.youtube.com/playlist?list=PL55RiY5tL51q4D-B63KBnygU6opNPFk_q) - Academind (Youtube)
 * [Express JS Crash Course](https://www.youtube.com/watch?v=L72fhGm1tfE) - Brad Traversy, Traversy Media (Youtube)
+* [Node and Express](https://fullstackopen.com/en/part3/node_js_and_express) - Full Stack Open
 * [Node and Express Tutorial](https://www.youtube.com/watch?v=TNV0_7QRDwY) - John Smilga, Coding Addict (YouTube)
 * [Node.js API Development for Beginners](https://www.udemy.com/course/node-js-api-tutorial/) (Udemy)
 * [Node.js Basics](https://www.youtube.com/playlist?list=PLqq-6Pq4lTTa-d0iZg41U2RDqECol9C5B) - Java Brains (Youtube)
@@ -467,6 +468,7 @@
 #### React
 
 * [Full-Stack Web Development with React Specialization](https://www.coursera.org/specializations/full-stack-react) - Jogesh K. Muppala (Coursera)
+* [Introduction to React](https://fullstackopen.com/en/part1/introduction_to_react) - Full Stack Open
 * [React](https://progate.com/languages/react) (progate) *(account required)*
 * [React basic in just 1 hour](https://www.udemy.com/course/react-basic-in-just-1-hour/) (Udemy)
 * [React Crash Course 2020](https://www.youtube.com/watch?v=4UZrsTqkcW4) - freecodecamp