light: add page (#1814)

pages/linux/light.md

@@ -0,0 +1,19 @@
+# light
+
+> CLI to control the backlight of your screen.
+
+- Get the current backlight value in percent:
+
+`light`
+
+- Set the backlight value to 50 percent:
+
+`light -S {{50}}`
+
+- Reduce 20 percent from the current backlight value:
+
+`light -U {{20}}`
+
+- Add 20 percent to the current backlight value:
+
+`light -A {{20}}`