Document `clear` slide type

docs/features.md

@@ -128,7 +128,7 @@ You can hide number manually:
 		</style>
 	</section>
 
-Some slide types could also hide slide number: `white` or `black`.
+Some slide type `clear` could also hide slide number.
 
 ### Types
 
@@ -136,18 +136,22 @@ Types are changing slide’s look. You can set type by adding class to the main
 
 #### White
 
-White type set white background and turns off slide number. Use it when you need just a pure white slide.
+White type set white background and turns off slide number. Use it when you need a white slide.
 
 	<section class="slide white">
 
 #### Black
 
-Black type set black background and turns off slide number. Use it when you need just a pure black slide.
+Black type set black background and turns off slide number. Use it when you need a black slide.
 
 	<section class="slide black">
 
 Please note that black slide type doesn’t change text color.
 
+#### Clear
+
+Clear type turns off slide number. Use it when you need a pure slide. May be mixed with `white` or `black` type.
+
 #### Grid
 
 Grid set a background with two guide types: main magenta guides and additional cyan guides, setting margins, rows and columns.