Clarify Rocket env var defaults

Mention `ROCKET_WORKERS`, but remove `ROCKET_ENV` since most users
probably wouldn't use it.

.env.template

@@ -258,10 +258,11 @@
 ## In any case, if a code has been used it can not be used again, also codes which predates it will be invalid.
 # AUTHENTICATOR_DISABLE_TIME_DRIFT=false
 
-## Rocket specific settings, check Rocket documentation to learn more
+## Rocket specific settings
-# ROCKET_ENV=staging
+## See https://rocket.rs/v0.4/guide/configuration/ for more details.
-# ROCKET_ADDRESS=0.0.0.0 # Enable this to test mobile app
+# ROCKET_ADDRESS=0.0.0.0
-# ROCKET_PORT=8000
+# ROCKET_PORT=80  # Defaults to 80 in the Docker images, or 8000 otherwise.
+# ROCKET_WORKERS=10
 # ROCKET_TLS={certs="/path/to/certs.pem",key="/path/to/key.pem"}
 
 ## Mail specific settings, set SMTP_HOST and SMTP_FROM to enable the mail service.