feat: specify Python versions required (PEP 345)

Author: Rogdham

CHANGELOG.md

@@ -26,6 +26,7 @@ adheres to [Semantic Versioning](https://semver.org/).
 
 ### :house: Internal
 
+- Specify the Python versions required in package metadata
 - Test the `mode` attribute of objects returned by `xz.open`/`XZFile`
 - Minor improvements in some docstrings
 

setup.cfg

@@ -18,6 +18,12 @@ classifiers =
     Operating System :: OS Independent
     Programming Language :: Python
     Programming Language :: Python :: 3
+    Programming Language :: Python :: 3 :: Only
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
+    Programming Language :: Python :: 3.10
     Topic :: Utilities
     Topic :: System :: Archiving
     Topic :: System :: Archiving :: Compression
@@ -26,6 +32,7 @@ classifiers =
 include_package_data = True
 package_dir = =src
 packages = xz
+python_requires = >=3.6
 setup_requires =
     setuptools_scm
     wheel