[css-inline] update CJK exclusion area text per #947

Author: dauwhe

css-inline-3/Overview.bs

@@ -955,15 +955,12 @@ Initial Letter Wrapping: the 'initial-letter-wrap' property</h3>
 		<dd>
 			This value is the same as ''initial-letter-wrap/none'',
 			except that the exclusion area of the impacted lines
-			is increased as necessary for its end-edge to land on the character grid.
+			is increased as necessary for its end-edge to land on the character grid,
+			i.e. to be a multiple of (''1ic'' + 'letter-spacing')
+			as computed on the containing block.
 			The 'justify-self' property can then be used to align
 			the initial letter box within the exclusion area.
 
-			The rule for matching the character grid is
-			''1ch'' &times; <var>n</var> + 'letter-spacing' &times; (<var>n</var> - 1),
-			where <var>n</var> is the size of the initial letter
-			as specified by the 'initial-letter' property.
-
 			<figure>
 				<img src="images/CJK-Initial.001.png" width="480"
 				     alt="Diagram of Japanese initial letter in vertical writing mode">