Remove confusing CSS equivs introduced in 77bbbb9

Author: lovell

README.md

@@ -334,8 +334,6 @@ resize the image to be as large as possible
 while ensuring its dimensions are less than or equal to
 the `width` and `height` specified.
 
-This is equivalent to using the `contain` value of the CSS `background-size` property.
-
 Both `width` and `height` must be provided via `resize` otherwise the behaviour will default to `crop`.
 
 #### min()
@@ -345,8 +343,6 @@ resize the image to be as small as possible
 while ensuring its dimensions are greater than or equal to
 the `width` and `height` specified.
 
-This is equivalent to using the `cover` value of the CSS `background-size` property.
-
 Both `width` and `height` must be provided via `resize` otherwise the behaviour will default to `crop`.
 
 #### background(rgba)