README: separates optional docker params

README.md

@@ -34,11 +34,12 @@ Configuration parameters are set by these docker environment variables:
 
 | parameter | description  |
 |---------|--------------|
-| **DISCOVERY_CONTEXT_ROOT** | root of the end-points |
 | **DB_URI** | DB which holds ObsTAP table |
 | **DB_USERNAME** | DB user which has access to ObsTAP |
 | **DB_PASSWORD** | and user's password |
-| **CUTOUT_SERVICE_URL** | URL of a SODA service presented in the response |
+| *optional:* |  |
+| **CUTOUT_SERVICE_URL** | URL in Service Descriptor of the VOTable response |
+| **DISCOVERY_CONTEXT_ROOT** | root of the end-points |
 
 
 ## vlkb-obscore