Update sensor.google_travel_time.markdown (#6125)

* Update sensor.google_travel_time.markdown

Google have removed the previous daily free API limit, instead requiring a billing account to be set up. Including details on limits and quotas and how to set them.

* Update sensor.google_travel_time.markdown

Updates as requested in feedback. Thanks

* Minor changes

* Again

source/_components/sensor.google_travel_time.markdown

@@ -13,11 +13,19 @@ ha_iot_class: "Cloud Polling"
 ha_release: 0.19
 ---
 
-Sensor to provide travel time from the [Google Distance Matrix API](https://developers.google.com/maps/documentation/distance-matrix/).
+The `google_travel_time` sensor provides travel time from the [Google Distance Matrix API](https://developers.google.com/maps/documentation/distance-matrix/).
+
+## {% linkable_title Setup %}
 
 You need to register for an API key by following the instructions [here](https://github.com/googlemaps/google-maps-services-python#api-keys). You only need to turn on the Distance Matrix API.
 
-A free API Key allows 2500 requests per day. The sensor will update the travel time every 5 minutes.
+[Google now require billing](https://mapsplatform.googleblog.com/2018/05/introducing-google-maps-platform.html) to be enabled (and a valid credit card loaded) to access Google Maps APIs. The Distance Matrix API is billed at US$10 per 1000 requests, however a US$200 per month credit is applied (20,000 requests). By default, the sensor will update the travel time every 5 minutes, making approximately 288 calls per day. Note that at this rate, more than 2 sensors will likely exceed the free credit amount. If you need to run more than 2 sensors, consider changing the [scan interval](/docs/configuration/platform_options/#scan-interval) to something longer than 5 minutes to stay within the free credit limit.
+
+A quota can be set against the API to avoid exceeding the free credit amount. Set the 'Elements per day' to a limit of 645 or less. Details on how to configure a quota can be found [here](https://developers.google.com/maps/documentation/distance-matrix/usage-and-billing#set-caps)
+
+## {% linkable_title Configuration %}
+
+To enable the sensor, add the following lines to your `configuration.yaml` file:
 
 ```yaml
 # Example entry for configuration.yaml
@@ -40,9 +48,9 @@ Configuration variables:
   - **arrival_time** (*Optional*): See notes above for `departure_time`. `arrival_time` can not be `now`, only a Unix timestamp or time string. You can not provide both `departure_time` and `arrival_time`. If you do provide both, `arrival_time` will be removed from the request.
   - **units** (*Optional*): Set the unit for the sensor in metric or imperial, otherwise the default unit the same as the unit set in `unit_system:`.
 
-##### {% linkable_title Dynamic Configuration %}
+## {% linkable_title Dynamic Configuration %}
 
-Tracking can be setup to track entities of type device_tracker, zone, and sensor. If an entity is placed in the origin or destination then every 5 minutes when the component updates it will use the latest location of that entity.
+Tracking can be setup to track entities of type `device_tracker`, `zone` and `sensor`. If an entity is placed in the origin or destination then every 5 minutes when the platform updates it will use the latest location of that entity.
 
 ```yaml
 # Example entry for configuration.yaml
@@ -67,10 +75,9 @@ sensor:
     destination: zone.home
     options:
       units: imperial    # 'metric' for Metric, 'imperial' for Imperial
-    
 ```
 
-#### {% linkable_title Entity Tracking %}
+## {% linkable_title Entity Tracking %}
 
 - **device_tracker**
   - If state is a zone then the zone location will be used