Update README.md

Author: kasparsj

README.md

@@ -99,21 +99,33 @@ Hex or rgb() color string.
 #### top
 **Type:** number or string (percentage or viewport units)
 
+Better use "y" where possible.
+
 #### left
 **Type:** number or string (percentage or viewport units)
 
+Better use "x" where possible.
+
 #### width
 **Type:** number or string (percentage or viewport units)
 
+Better use "scaleX" where possible.
+
 #### height
 **Type:** number or string (percentage or viewport units)
 
+Better use "scaleY" where possible.
+
 #### backgroundPositionX
 **Type:** number or string (percentage or viewport units)
 
+Better use "x" where possible.
+
 #### backgroundPositionY
 **Type:** number or string (percentage or viewport units)
 
+Better use "y" where possible.
+
 ### Options
 
 Options can be specified for all properties: