Added an unsupported warning on startup if using Python 3.9

bazarr.py

@@ -20,6 +20,9 @@ def check_python_version():
         print("Python " + minimum_py3_str + " or greater required. "
               "Current version is " + platform.python_version() + ". Please upgrade Python.")
         sys.exit(1)
+    elif int(python_version[0]) == 3 and int(python_version[1]) == 9:
+        print("Python 3.9.x is unsupported. Current version is " + platform.python_version() +
+              ". Keep in mind that even if it works, you're on your own.")
     elif (int(python_version[0]) == minimum_py3_tuple[0] and int(python_version[1]) < minimum_py3_tuple[1]) or \
             (int(python_version[0]) != minimum_py3_tuple[0]):
         print("Python " + minimum_py3_str + " or greater required. "