Added water heater doc. (#113)

* Added water heater doc.

* Fixed merge error

* Added states, methods, and operation modes note.

docs/entity_water_heater.md

@@ -0,0 +1,45 @@
+---
+title: Water Heater Entity
+sidebar_label: Water Heater
+---
+
+## 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
+| ---- | ---- | ------- | -----------
+| min_temp | float | 110°F | The minimum temperature that can be set.
+| max_temp | float | 140°F | The maximum temperature that can be set.
+| temperature | float | none | The current temperature in °C or °F.
+| operation_mode | string | none | The current operation mode.
+| operation_list | list | none | List of possible operation modes.
+| away_mode | string | none | The current status of away mode. (on, off)
+
+The allowed operation modes are specified in the base component and implementations of the water_heater component cannot differ.
+
+Properties have to follow the units defined in the `unit_system`.
+
+## States
+| State | Description
+| ----- | -----------
+| `STATE_ECO` | Energy efficient mode, provides energy savings and fast heating.
+| `STATE_ELECTRIC` | Electric only mode, uses the most energy.
+| `STATE_PERFORMANCE` | High performance mode.
+| `STATE_HIGH_DEMAND` | Meet high demands when water heater is undersized.
+| `STATE_HEAT_PUMP` | Slowest to heat, but uses less energy.
+| `STATE_GAS` | Gas only mode, uses the most energy.
+| `STATE_OFF` | The water heater is off.
+
+## Methods
+### `set_temperature` or `async_set_temperature`
+Sets the temperature the water heater should heat water to.
+
+### `set_operation_mode`or `async_set_operation_mode`
+Sets the operation mode of the water heater. Must be in the operation_list.
+
+### `turn_away_mode_on` or `async_turn_away_mode_on`
+Set the water heater to away mode.
+
+### `turn_away_mode_off` or `async_turn_away_mode_off`
+Set the water heater back to the previous operation mode. Turn off away mode.

website/i18n/en.json

@@ -217,6 +217,10 @@
         "title": "Vacuum Entity",
         "sidebar_label": "Vacuum"
       },
+      "entity_water_heater": {
+        "title": "Water Heater Entity",
+        "sidebar_label": "Water Heater"
+      },
       "entity_weather": {
         "title": "Weather Entity",
         "sidebar_label": "Weather"

website/sidebars.json

@@ -20,6 +20,7 @@
       "entity_sensor",
       "entity_switch",
       "entity_vacuum",
+      "entity_water_heater",
       "entity_weather"
     ],
     "Authentication": [