Add arguments to command.

setup.py

@@ -24,7 +24,7 @@ setup(
     ],
     entry_points='''
         [console_scripts]
-        synthale=synthale.cli:cli
+        synthale=synthale.cli:main
     ''',
     classifiers=[
         'Development Status :: 2 - Pre-Alpha',

src/synthale/cli.py

@@ -3,7 +3,13 @@
 import click
 
 
-@click.group()
-def cli():
-    """Synthale generates Markdown files from BeerXML files."""
+@click.command()
+@click.argument('input')
+@click.argument('output')
+def main(input, output):
+    """Generate markdown files from BeerXML files.
+
+    INPUT is either a directory containing XML files, or an individual XML
+    file. OUTPUT is the directory to write the markdown files to.
+    """
     pass