chore: restoring the file for demo purposes

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

Author: anthonydmays

lesson_13/README.md

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+# Lesson 13: Data Structures: Maps and Sets ([Slides](https://code-differently.github.io/code-differently-25-q1/slides/#/lesson_13))
+
+## 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
+
+- [ ] Implement the `findPermutationDifference` method in [Lesson13.java](./maps_java/maps_app/src/main/java/com/codedifferently/lesson13/Lesson13.java).
+- [ ] Do pre-work for [lesson 14](/lesson_14/).
+
+## Extra Credit
+
+- [ ] Implement the TypeScript version in [lesson13.ts](./maps_ts/src/lesson13.ts).