Add- "Introduction to React Native" Course (#5670)

* Add "Data Structures and Algorithms Specialization" link

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

courses/free-courses-en.md

@@ -482,6 +482,7 @@
 #### React Native
 
 * [CS50's Mobile App Development with React Native](https://www.edx.org/course/cs50s-mobile-app-development-with-react-native) - edX
+* [Introduction to React Native](https://fullstackopen.com/en/part10/introduction_to_react_native) - Full Stack Open
 * [React Native for Beginners](https://www.youtube.com/playlist?list=PL4cUxeGkcC9ixPU-QkScoRBVxtPPzVjrQ) - The Net Ninja
 * [React Tutorial for Beginners](https://www.youtube.com/playlist?list=PLC3y8-rFHvwgg3vaYJgHGnModB54rxOk3) - codevolution