Created brightness (markdown)

brightness.md

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+[<- widgets](https://github.com/copycat-killer/lain/wiki/Widgets)
+
+Shows brightness level in a textbox.
+
+	volumewidget = lain.widgets.contrib.brightness()
+
+### input table
+
+Variable | Meaning | Type | Default
+--- | --- | --- | ---
+`timeout` | Refresh timeout seconds | int | 5
+`backlight` | Backlight Video | string | "acpi_video0" 
+`settings` | User settings | function | empty function
+
+`settings` can use the following variables:
+
+Variable | Meaning | Type | Values
+--- | --- | --- | ---
+`brightness_now` | Brightness level | int | 0-100
+
+### output table
+
+Variable | Meaning | Type
+--- | --- | --- 
+`widget` | The widget | `wibox.widget.textbox`
+`update` | Update `widget` | function
+
+You can control the widget with key bindings like these:
+
+    -- Volume control
+    awful.key({}, "XF86MonBrightnessUp",
+    function ()
+        awful.util.spawn("xbacklight -inc 1")
+        brightnesswidget.update()
+    end),
+    awful.key({}, "XF86MonBrightnessDown",
+    function ()
+        awful.util.spawn("xbacklight -dec 1")
+        brightnesswidget.update()
+    end),