Add docs for conn_max_age setting

Author: tyler-8

README.adoc

@@ -147,6 +147,15 @@ section for more information on configuring the database.
 
 Note that these are used to configure `DATABASE` in `configuration.py`.
 
+[source,yaml]
+----
+netbox_database_conn_age: 300
+----
+
+To configure Netbox to keep database connections open longer than a single requests,
+set `netbox_database_conn_age` to your preferred maximum connection age, in seconds.
+300 seconds (5 minutes) is typically a good number to start with.
+
 [source,yaml]
 ----
 netbox_redis_host: 127.0.0.1