Add IoTaWatt integration doc (#18787)

source/_integrations/iotawatt.markdown

@@ -0,0 +1,19 @@
+---
+title: IoTaWatt
+description: Instructions on how to integrate IoTaWatt into Home Assistant.
+ha_release: 2021.9
+ha_category:
+  - Energy
+ha_iot_class: Local Polling
+ha_config_flow: true
+ha_domain: iotawatt
+ha_codeowners:
+  - '@gtdiehl'
+ha_platforms:
+  - sensor
+---
+A sensor platform for the [IoTaWatt](https://www.iotawatt.com/) Open WiFi Electricity Monitor. It 
+will collect data from the Current Transformer Clamps (Input CTs) and any Outputs that are defined on the IoTaWatt
+and create them as sensors in Home Assistant.
+
+{% include integrations/config_flow.md %}