indicate compatibility with Python 3.10 in setup.py

Author: boegel

setup.py

@@ -116,6 +116,7 @@ def find_rel_test():
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Topic :: Software Development :: Build Tools",
     ],
     platforms="Linux",