Chore: Adjust minimum Python version in project metadata

Author: amotl

setup.py

@@ -77,7 +77,7 @@ def read(path):
         doc=['sphinx>=3.5,<7',
              'crate-docs-theme>=0.26.5'],
     ),
-    python_requires='>=3.7',
+    python_requires='>=3.6',
     package_data={'': ['*.txt']},
     classifiers=[
         'Development Status :: 5 - Production/Stable',
@@ -86,6 +86,7 @@ def read(path):
         'Operating System :: OS Independent',
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',