docs(config): document timer max ring seconds configuration (#277)

.env.example

@@ -54,6 +54,9 @@ LVA_PULSE_COOKIE="/run/user/${LVA_USER_ID}/pulse/cookie"
 ### Stop model (optional):
 # STOP_MODEL="stop"
 
+### Seconds after which the timer stops ringing (optional):
+# TIMER_MAX_RING_SECONDS="900"
+
 ### Refactory seconds (optional):
 # REFACTORY_SECONDS="2"