Update keywords for PyPI (#10)

Author: jugmac00

setup.cfg

@@ -27,7 +27,7 @@ classifiers =
     Programming Language :: Python :: Implementation :: CPython
     Topic :: Documentation
     Topic :: Documentation :: Sphinx
-keywords = tox, formatter
+keywords = sphinx, argparse
 project_urls =
     Source=https://github.com/gaborbernat/sphinx-argparse-cli
     Tracker=https://github.com/gaborbernat/sphinx-argparse-cli/issues