Require Python version >= 3.7.0

Spawned from #81, but for using the same Python version as the Blinka requirement of >= 6.20.6

Author: tekktrik

setup.py

@@ -34,6 +34,7 @@
     # Author details
     author="Adafruit Industries",
     author_email="circuitpython@adafruit.com",
+    python_requires=">=3.7.0",
     install_requires=["Adafruit-Blinka>=6.20.4", "adafruit-circuitpython-typing"],
     # Choose your license
     license="MIT",