Clean up E0579 explanation

src/librustc_error_codes/error_codes/E0579.md

@@ -1,7 +1,4 @@
-When matching against an exclusive range, the compiler verifies that the range
-is non-empty. Exclusive range patterns include the start point but not the end
-point, so this is equivalent to requiring the start of the range to be less
-than the end of the range.
+A lower range wasn't less than the upper range.
 
 Erroneous code example:
 
@@ -17,3 +14,8 @@ fn main() {
     }
 }
 ```
+
+When matching against an exclusive range, the compiler verifies that the range
+is non-empty. Exclusive range patterns include the start point but not the end
+point, so this is equivalent to requiring the start of the range to be less
+than the end of the range.