Update free-courses-en.md (#10738)

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

* Update free-courses-en.md

courses/free-courses-en.md

@@ -779,6 +779,7 @@
 ### Graph Theory
 
 * [Graph Theory](https://youtube.com/playlist?list=PLztBpqftvzxXBhbYxoaZJmnZF6AUQr1mH) - Wrath of Math
+* [Graph Theory](https://nptel.ac.in/courses/111106102) - Prof. Soumen Maity (NPTEL)
 * [Graph Theory - DM](https://youtube.com/playlist?list=PLYrahs7hsYIQiSNxTfZndQz7jWPXsA1ur) - SCCI Labs IIT Ropar
 * [Graph Theory Playlist](https://youtube.com/playlist?list=PLDV1Zeh2NRsDGO4--qE8yH72HFL1Km93P) - WilliamFiset