Document the per-driver budget in the simulator example

The custom example ran 20 vehicles every 2s, which is 40x the one report per
5s the server allows for the single shared login.

Author: omlahore

docs/development.md

@@ -139,9 +139,15 @@ make simulate
 Custom example:
 
 ```bash
-go run ./cmd/simulator -url http://localhost:8080 -vehicles 20 -interval 2s -duration 2m
+go run ./cmd/simulator -url http://localhost:8080 -vehicles 1 -interval 6s -duration 2m
 ```
 
+The server allows one location report per driver per 5 seconds, and every
+simulated vehicle authenticates with the same login, so they share a single
+budget. Raising `-vehicles` without raising `-interval` to match just turns the
+extra reports into `429`s. The simulator warns at startup when the two do not
+fit.
+
 ## API Sanity Checks
 
 ### Submit one location