Standardization for weather components (#12)

* Create component_weather.md

also have to link it somewhere

"breaking" changes:
- datetime to UNIX timestamp
- pressure -> air_pressure
- wind_bearing now in letters only

* Update component_weather.md

* Update component_weather.md

* Use correct template

* Update entity_weather.md

docs/entity_weather.md

@@ -0,0 +1,53 @@
+---
+title: Weather Entity
+sidebar_label: Weather
+---
+
+## Properties
+
+> Properties should always only return information from memory and not do I/O (like network requests). Implement `update()` or `async_update()` to fetch data.
+
+| Name | Type | Default | Description
+| ---- | ---- | ------- | -----------
+| state | string | **Required** | The current weather condition.
+| temperature | float | **Required** | The current temperature in °C or °F.
+| air_pressure | float | `None` | The current air pressure in hPa.
+| humidity | float | `None` | The current humidity in %.
+| visibility | float | `None` | The current visibility in km or mi.
+| wind_speed | float | `None` | The current wind speed in km/h or mi/h.
+| wind_bearing | string | `None` | The current wind bearing, 1-3 letters.
+| forecast | array | `None` | Daily or Hourly forecast data.
+| attribution | string | `None` | The branding text required by the API provider.
+
+Properties have to follow the units defined in the `unit_system`.
+
+### Forecast
+
+Forecast data should either be daily or hourly.
+
+| Name | Type | Default | Description
+| ---- | ---- | ------- | -----------
+| datetime | string | **Required** | UTC Date time in RFC 3339 format.
+| temperature | float | **Required** | The higher temperature in °C or °F
+| condition | string | `None` | The weather condition at this point.
+| templow | float | `None` | The lower daily Temperature in °C or °F
+
+### Recommended values for state and condition
+
+These weather conditions are included in our translation files and also show the corresponding icon.
+
+| Condition | Description
+| --------- | -----------
+| clear-night | Clear night
+| cloudy | Many clouds
+| fog | Fog
+| lightning | Lightning/ thunderstorms
+| lightning-rainy | Lightning/ thunderstorms and rain
+| partlycloudy | A few clouds
+| pouring | Pouring rain
+| rainy | Rain
+| snowy | Snow
+| snowy-rainy | Snow and Rain
+| sunny | Sunshine
+| windy | Wind
+| windy-variant | Wind and clouds

website/sidebars.json

@@ -10,7 +10,8 @@
       "entity_index",
       "entity_binary_sensor",
       "entity_sensor",
-      "entity_switch"
+      "entity_switch",
+      "entity_weather"
     ],
     "Configuration.yaml": [
       "configuration_yaml_index"