Add note about containers (#6511)

source/_components/sensor.cpuspeed.markdown

@@ -16,6 +16,13 @@ ha_iot_class: "Local Push"
 
 The `cpuspeed` sensor platform to allow you to monitor the current CPU speed.
 
+
+<p class='note warning'>
+  You can't use this sensor in a Container (like Hass.io) as it requires access to the physical CPU. Also, not all [ARM CPUs](https://github.com/workhorsy/py-cpuinfo/#cpu-support) are supported.
+</p>
+
+## {% linkable_title Configuration %}
+
 To add this platform to your installation, add the following to your `configuration.yaml` file:
 
 ```yaml
@@ -24,6 +31,10 @@ sensor:
   - platform: cpuspeed
 ```
 
-Configuration variables:
-
-- **name** (*Optional*): Name of the sensor.
+{% configuration %}
+name:
+  description: Name to use in the frontend.
+  required: false
+  type: string
+  default: CPU speed
+{% endconfiguration %}