README.md in routemaster-drain-3.6.3 vs README.md in routemaster-drain-3.6.4

@@ -262,9 +262,12 @@
 
 ```ruby
 $cache = Routemaster::Cache.new(client_options: {source_peer: "<your user agent>"})
 ```
 
+You can specify your user agent with the `ROUTEMASTER_API_CLIENT_USER_AGENT` environment
+variable as well.
+
 ### Expire Cache data for all notified resources
 
 You may wish to maintain a coherent cache, but don't need the cache to be warmed
 before you process incoming events. In that case, use the cache as detailed above
 but swap the `Caching` drain out for `CacheBusting`