docs(readme): add documentation for example plugin

README.md

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+# Example
+
+Example is a minimal reference plugin that demonstrates the common Noctalia
+plugin entry types: a bar widget, a headless service, and a control-center
+shortcut.
+
+## Plugin
+
+| Field | Value |
+| --- | --- |
+| ID | `noctalia/example` |
+| Entries | Bar widgets: `hello`, `declarative`; service: `ticker`; shortcut: `toggle` |
+
+## Usage
+
+Add the `hello` widget from the Add-widget picker. The widget displays a
+configurable label and glyph, counts clicks, reads `data.txt`, and watches the
+shared `tick` state published by the `ticker` service.
+
+Add the `declarative` widget to see the same service tick rendered as a
+`ui.*` tree via `barWidget.render()` — a glyph, the live counter in a filled
+rounded badge (impossible with the imperative API), and an inline `ui.button`
+whose click is handled separately from the widget-level `onClick`. Simple
+widgets can keep using `setText`/`setGlyph`; `render()` is the declarative
+alternative for composite content.
+
+Add the `toggle` shortcut from Settings -> Control Center shortcuts. It toggles
+shared plugin state and shows how shortcut entries can render an active state.
+
+## Settings
+
+| Setting | Type | Default | Description |
+| --- | --- | --- | --- |
+| `label` | `string` | `Hello` | Text shown in the bar widget. |
+| `glyph` | `glyph` | `puzzle` | Glyph shown before the label. |
+| `show_glyph` | `bool` | `true` | Controls whether the glyph is visible. |
+
+## IPC
+
+The `hello` widget exposes two IPC events:
+
+```sh
+noctalia msg plugin noctalia/example:hello focused set "Hi there"
+noctalia msg plugin noctalia/example:hello focused fetch "https://example.com"
+```
+
+`set` updates the widget label at runtime. `fetch` performs an asynchronous HTTP
+request and reports the response status in a notification.
+
+You can open the example panel with the following IPC call:
+
+```sh
+noctalia msg panel-toggle noctalia/example:panel
+```