Add docs and remove unused import

bin/app-json.py

@@ -1,7 +1,13 @@
 #!/usr/bin/env python3
 
+# Usage: ./app-json.py
+#
+# Gather metadata from Co-op Cloud apps in $ABRA_DIR/apps (default
+# ~/.abra/apps), and format it as JSON so that it can be hosted here:
+# https://abra-apps.autonomic.zone
+
 from json import dump
-from os import chdir, getcwd, listdir, mkdir
+from os import chdir, listdir, mkdir
 from os.path import exists, expanduser
 from pathlib import Path
 from re import findall, search