Add documentation for wiffi integration (#11748)

source/_integrations/wiffi.markdown

@@ -0,0 +1,30 @@
+---
+title: STALL WIFFI
+logo: wiffi.png
+description: Support for WIFFI devices from stall.biz, e.g., Weatherman, Rainyman, ...
+featured: true
+ha_category:
+  - DIY
+ha_release: 0.109
+ha_iot_class: Local Push
+ha_config_flow: true
+ha_codeowners:
+  - '@mampfes'
+---
+
+This integration allows you to connect your [STALL WIFFI](https://stall.biz) devices directly to Home Assistant.
+
+## Configuration via the frontend
+
+Menu: **Configuration** -> **Integrations**.
+
+Click on the `+` sign to add an integration and click on **STALL WIFFI**.
+After completing the configuration flow, the STALL WIFFI
+integration will be available.
+
+## Configure the WIFFI device
+
+1. Set "CCU-IP Adresse myCCUIP" to the IP address of Home Assistant.
+2. Set port for JSON telegrams to configured server port using parameter "send_json".
+
+Home Assistant will open a TCP server socket on the configured port and listens for incoming telegrams from STALL WIFFI devices. Entities from new devices will be automatically added.