Update readme

README.md

@@ -15,14 +15,14 @@ them into a BaseStation format network feed.
 ### OpenSky Options
 | Option              | Value    | Description |
 | -                   | -        | -           |
-| ```-user```         | text     | OpenSky network username |
+| ```-user```         | text     | OpenSky network username (defaults to anonymous access) |
 | ```-password```     | text     | OpenSky network password |
 | ```-anonRootUrl```  | url      | Root URL for anonymous OpenSky API calls (defaults to ```https://opensky-network.org/api```) |
 | ```-userRootUrl```  | url      | Root URL for logged-in OpenSky API calls (defaults to ```https://{user}:{password}@opensky-network.org/api```) |
 | ```-anonInterval``` | seconds  | Seconds between fetches for anonymous users (defaults to ```10```) |
 | ```-userInterval``` | seconds  | Seconds between fetches for logged-in users (defaults to ```5```) |
-| ```-icao24```       | hex-list | Hyphen-separated ICAOs to fetch from OpenSky |
-| ```-lamin```        | degrees  | Lower bound for latitude |
+| ```-icao24```       | hex-list | Hyphen-separated ICAOs to fetch from OpenSky (defaults to all aircraft) |
+| ```-lamin```        | degrees  | Lower bound for latitude (defaults to no bounding box) |
 | ```-lamax```        | degrees  | Upper bound for latitude |
 | ```-lomin```        | degrees  | Lower bound for longitude |
 | ```-lomax```        | degrees  | Upper bound for longitude |