Update README.md

Documented the use of the ABC module in src/ingame/objects.py.

Author: the-tl

README.md

@@ -105,7 +105,7 @@ Simple `tkinter` window with key event binding:
 ## 🛠️ Development Notes
 
 Written in Python 3.10+
-Uses `tkinter`, `Enum`, and `inspect`.
+Uses `tkinter`, `Enum`, `abc`, and `inspect`.
 
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