Documentation rework

documentation/en/feature-central-mode.md

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+# Centralized Control
+
+- [Centralized Control](#centralized-control)
+  - [Configuration of Centralized Control](#configuration-of-centralized-control)
+  - [Usage](#usage)
+
+This feature allows you to control all your _VTherms_ from a single control point.
+A typical use case is when you leave for an extended period and want to set all your _VTherms_ to frost protection, and when you return, you want to set them back to their initial state.
+
+Centralized control is done from a special _VTherm_ called centralized configuration. See [here](creation.md#centralized-configuration) for more information.
+
+## Configuration of Centralized Control
+
+If you have set up a centralized configuration, you will have a new entity named `select.central_mode` that allows you to control all _VTherms_ with a single action.
+
+![central_mode](images/central-mode.png)
+
+This entity appears as a list of choices containing the following options:
+1. `Auto`: the 'normal' mode where each _VTherm_ operates autonomously,
+2. `Stopped`: all _VTherms_ are turned off (`hvac_off`),
+3. `Heat only`: all _VTherms_ are set to heating mode if supported, otherwise they are stopped,
+4. `Cool only`: all _VTherms_ are set to cooling mode if supported, otherwise they are stopped,
+5. `Frost protection`: all _VTherms_ are set to frost protection mode if supported, otherwise they are stopped.
+
+## Usage
+
+For a _VTherm_ to be controllable centrally, its configuration attribute named `use_central_mode` must be true. This attribute is available in the configuration page `Main Attributes`.
+
+![central_mode](images/use-central-mode.png)
+
+This means you can control all _VTherms_ (those explicitly designated) with a single control.