feat: actually add lesson_13 pre-work

Signed-off-by: Anthony D. Mays <[email protected]>

Author: anthonydmays

lesson_13/README.md

@@ -0,0 +1,12 @@
+# Lesson 13: Data Structures: Maps and Sets
+
+## Pre-work
+
+Please review the following resources before lecture:
+
+* [Map and HashMap in Java - Full Tutorial (Video)](https://www.youtube.com/watch?v=H62Jfv1DJlU)
+* [Maps vs. Objects in JavaScript - What's the Difference? (Video)](https://www.youtube.com/watch?v=cU84h71ufqE)
+
+## Homework
+
+TODO(anthonydmays): Implement this