Added documentation for nina (#19472)

* Added documentation for nina

* Update source/_integrations/nina.markdown

Co-authored-by: Marvin Wichmann <marvin@fam-wichmann.de>

* Formulations modified and version changed

Co-authored-by: Marvin Wichmann <marvin@fam-wichmann.de>

source/_integrations/nina.markdown

@@ -0,0 +1,20 @@
+---
+title: NINA
+description: Instructions on how to set up NINA warnings in Home Assistant.
+ha_category:
+  - Binary Sensor
+ha_release: 2022.2
+ha_iot_class: Cloud Polling
+ha_config_flow: true
+ha_codeowners:
+  - '@DeerMaximum'
+ha_domain: nina
+ha_platforms:
+  - binary_sensor
+---
+
+The [NINA](https://www.bbk.bund.de/DE/Warnung-Vorsorge/Warn-App-NINA/warn-app-nina_node.html) integration displays warnings from the [Bundesamt für Bevölkerungsschutz und Katastrophenhilfe](https://www.bbk.bund.de/) in Germany.
+
+For each county/city it creates warning slots that change to Unsafe when warnings are present. The text of the warning and the metadata are stored in the attributes of the slots.
+
+{% include integrations/config_flow.md %}