Added Graph Theory Course Playlist By WilliamFiset (#10150)

* Update free-courses-en.md

* 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

@@ -730,6 +730,7 @@
 
 * [Graph Theory](https://youtube.com/playlist?list=PLztBpqftvzxXBhbYxoaZJmnZF6AUQr1mH) - Wrath of Math
 * [Graph Theory - DM](https://youtube.com/playlist?list=PLYrahs7hsYIQiSNxTfZndQz7jWPXsA1ur) - SCCI Labs IIT Ropar
+* [Graph Theory Playlist](https://youtube.com/playlist?list=PLDV1Zeh2NRsDGO4--qE8yH72HFL1Km93P) - WilliamFiset
 
 
 ### Haskell