docs: update readme

README.md

@@ -18,12 +18,22 @@ aarel server        # launch the server for the detected beamline
 ```
 
 Each command has a single-letter alias (`p`, `g`, `s`). `--config <path>`
-selects a different config file; it defaults to `data/defaults.json`.
+selects a different config file; it defaults to `/etc/aarel/defaults.json`.
 
 ### Launching
 
-`gui` and `server` pick their config entry from the detected beamline. Use
-`--entry <name>` to launch a different one.
+`gui` and `server` default to the deployment for the detected beamline. Pass
+`-d`/`--deployment <name>` to launch a specific one:
+
+```
+aarel gui -d x10sa                      # launch the x10sa GUI
+aarel server -d mytest                  # launch a custom deployment's server
+aarel server --deployment x06da --env-file ./dev.env
+```
+
+Deployments found under `deployments_base` are offered alongside the configured
+beamlines, so `-d` accepts either a configured beamline name or a discovered
+deployment.
 
 ## Development