Updated BT Home Hub 5 Device Tracker Documentation (#5964)

* Changed host to optional to fit an impending pull request that is about to be closed

Pull Request: home-assistant/core#15096

* Made Optional Italic

source/_components/device_tracker.bt_home_hub_5.markdown

@@ -25,6 +25,6 @@ device_tracker:
 
 Configuration variables:
 
-- **host** (*Required*): The IP address of your router, e.g., 192.168.1.254.
+- **host** (*Optional*): The IP address of your router, Default: 192.168.1.254.
 
 See the [device tracker component page](/components/device_tracker/) for instructions how to configure the people to be tracked.