Change "more power" to "more powerful"

Fixes a grammatical error in `appearance.md`.

docs/config/appearance.md

@@ -485,7 +485,7 @@ See [Styling Inactive Panes](#style-inactive-panes) for more information
 on hue, saturation, brigthness transformations.
 
 If you'd like to have control over scaling, tiling/repeating, scrolling
-behavior and more, take a look at the more power
+behavior and more, take a look at the more powerful
 [background](lua/config/background.md) configuration option.
 
 ## Window Background Gradient