add the cli functionality

url2markdown/cli.py

@@ -0,0 +1,11 @@
+import argparse
+
+
+def cli():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("URL",
+                        help="The URL of the article to convert to Markdown.",
+                        type=str)
+    parser.add_argument("--topics", help="A list of comma separated topics.")
+    return parser.parse_args()
+