Document the error pages dir

staticshield.py

@@ -33,6 +33,7 @@ Session(app)
 # Verify the required configuration
 # SERVE_DIR: Base dir of the files we want to serve; Flask will take care not to escape this dir
 # MOTHERSHIP: Mothership server and login-url, which will redirect here with a sessionstart/SEKRIT
+# ERROR_PAGES_DIR: (optional) Base dir of 403.html, 404.html to show as alternative to default short error message
 config_vars = ['SERVE_DIR', 'MOTHERSHIP', 'ERROR_PAGES_DIR']
 for config_var in config_vars:
     if config_var not in app.config: