Adds video description.

README.md

@@ -760,8 +760,8 @@ if you can identify the runtime complexity of different algorithms. It's a super
 ## Trees
 
 - ### Trees - Intro
-    - [ ] [Intro to Trees](https://www.coursera.org/lecture/data-structures/trees-95qda)
-    - [ ] [Tree Traversal](https://www.coursera.org/lecture/data-structures/tree-traversal-fr51b)
+    - [ ] [Intro to Trees (video)](https://www.coursera.org/lecture/data-structures/trees-95qda)
+    - [ ] [Tree Traversal (video)](https://www.coursera.org/lecture/data-structures/tree-traversal-fr51b)
     - [ ] [BFS(breadth-first search) and DFS(depth-first search) (video)](https://www.youtube.com/watch?v=uWL6FJhq5fM)
         - BFS notes:
            - level order (BFS, using queue)