note on authentication & configuration

README.md

@@ -6,6 +6,14 @@ gridscale-support has not been merged yet, it imports libretto from here:
 
 [https://g.hazardous.org/fkr/libretto](https://g.hazardous.org/fkr/libretto)
 
+The check-command looks in ```config/check.toml``` for a config file containing (for now) just the
+gridscale user and token. These can also be set via the environment:
+
+```
+GRIDSCALE_USER='userid'
+GRIDSCALE_TOKEN='token'
+```
+
 ## commands
 
 ### snapshots