Add documentation for AEMET OpenData integration (#16173)

source/_integrations/aemet.markdown

@@ -0,0 +1,66 @@
+---
+title: AEMET OpenData
+description: Instructions on how to integrate AEMET OpenData within Home Assistant.
+ha_release: 2021.3
+ha_category:
+  - Weather
+  - Sensor
+ha_iot_class: Cloud Polling
+ha_config_flow: true
+ha_codeowners:
+  - '@noltari'
+ha_domain: aemet
+---
+
+The AEMET weather platform uses [AEMET OpenData](https://opendata.aemet.es/) as a source for current meteorological data for your location. AEMET stands for "Agencia Estatal de Meteorología", which is the Spanish Meteorological Agency.
+
+There is currently support for the following device types within Home Assistant:
+
+- Sensor
+- Weather
+
+You need an API key, which is free but requires a [registration](https://opendata.aemet.es/centrodedescargas/altaUsuario).
+The AEMET OpenData service is completely free but is limited to the Spanish territory.
+
+## Configuration
+
+To add AEMET OpenData integration go to **Configuration** >> **Integrations** and find the integration in the list.
+
+{% configuration_basic %}
+API Key:
+  description: "API Key from the website"
+Name:
+  description: "Name of the integration"
+Latitude:
+  description: "Latitude for weather forecast and sensor"
+Longitude:
+  description: "Longitude for weather forecast and sensor"
+{% endconfiguration_basic %}
+
+The integration creates one weather entity per forecast mode and also sensors for all available conditions. There are two forecast modes, `daily` for daily forecast up to 6 days or `hourly` for an hourly forecast up to 3 days.
+
+For each condition, the following sensors are created:
+
+| Condition           | Description                          |
+| :------------------ | :----------------------------------- |
+| condition           | Current weather condition code.      |
+| humidity            | Relative humidity.                   |
+| pressure            | Sea-level air pressure in millibars. |
+| rain                | Rain volume.                         |
+| rain_probability    | Probability of rain.                 |
+| snow                | Snow volume.                         |
+| snow_probability    | Probability of snow.                 |
+| station_id          | Closest AEMET station ID.            |
+| station_name        | Closest AEMET station name.          |
+| station_timestamp   | Timestamp of AEMET station data.     |
+| storm_probability   | Probability of storm.                |
+| temperature         | Current temperature.                 |
+| temperature_feeling | Relative temperature.                |
+| town_id             | Closest AEMET town ID.               |
+| town_name           | Closest AEMET town name.             |
+| town_timestamp      | Timestamp of AEMET town data.        |
+| wind_bearing        | Wind bearing.                        |
+| wind_max_speed      | Max Wind speed.                      |
+| wind_speed          | Wind speed.                          |
+
+Details about the API are available in the [AEMET OpenData documentation](https://opendata.aemet.es/dist).