setup.cfg: add classifiers

Author: efiop

setup.cfg

@@ -5,6 +5,13 @@ description = SSH Filesystem -- Async SSH/SFTP backend for fsspec
 license = Apache License 2.0
 long_description = file: README.md
 long_description_content_type = text/markdown
+classifiers =
+    Development Status :: 4 - Beta
+    Programming Language :: Python :: 3
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
+    Programming Language :: Python :: 3.10
 
 [options]
 install_requires =