docs: add MyPy CI badge to the README for better visibility

Author: thalissonvs

README.md

@@ -9,6 +9,7 @@
     <img src="https://github.com/thalissonvs/pydoll/actions/workflows/tests.yml/badge.svg" alt="Tests">
     <img src="https://github.com/thalissonvs/pydoll/actions/workflows/ruff-ci.yml/badge.svg" alt="Ruff CI">
     <img src="https://github.com/thalissonvs/pydoll/actions/workflows/release.yml/badge.svg" alt="Release">
+    <img src="https://github.com/thalissonvs/pydoll/actions/workflows/mypy.yml/badge.svg" alt="MyPy CI">
 </p>
 
 <p align="center">