docs: Added reference to video from lecture

Author: anthonydmays

lesson_15/README.md

@@ -1,5 +1,9 @@
 # Lesson 15
 
+## Lecture Resources
+
+* [What is the OSI Model and Is It Still Relevant?](https://youtu.be/qiHCdgSo9zs)
+
 ## Homework
 
 * Read HFDP 9
@@ -14,4 +18,4 @@ For this assignment, you will build a NodeJS web server using the TypeScript pro
 * [Serving static files in Express](https://expressjs.com/en/starter/static-files.html)
 * [Serving static files example on GitHub](https://github.com/expressjs/express/tree/master/examples/static-files)
 
-[lesson-01]: /lesson_01/
+[lesson-01]: /lesson_01/