* Clarify the backlight_level API doc slightly
* review
|`backlight_step()` |Cycle through backlight levels |
|`backlight_increase()` |Increase the backlight level |
|`backlight_decrease()` |Decrease the backlight level |
-|`backlight_level(x)` |Sets the backlight level to specified level |
+|`backlight_level(x)` |Sets the backlight level, from 0 to |
+| |`BACKLIGHT_LEVELS` |
|`get_backlight_level()` |Return the current backlight level |
|`is_backlight_enabled()`|Return whether the backlight is currently on |