Update README to clarify comparator function

README.md

@@ -13,14 +13,24 @@ Marino](https://github.com/mgmarino) for, ironically, pointing out bugs.
 Example
 -------
 
-    var bs = require("binary-search");
-    bs([1, 2, 3, 4], 3, function(a, b) { return a - b; }); // => 2
-    bs([1, 2, 4, 5], 3, function(a, b) { return a - b; }); // => -3
+```js
+var bs = require("binary-search");
+
+bs([1, 2, 3, 4], 3, function(element, needle) { return element - needle; });
+// => 2
+
+bs([1, 2, 4, 5], 3, function(element, needle) { return element - needle; });
+// => -3
+```
 
 Be advised that passing in a comparator function is *required*. Since you're
 probably using one for your sort function anyway, this isn't a big deal.
 
-The 3rd and 4th arguments to the comparator are the current index and array, respectively. You shouldn't normally need the index or array to compare values, but it's there if you do.
+The comparator takes a 1st and 2nd argument of element and needle, respectively.
+
+The comparator also takes a 3rd and 4th argument, the current index and array,
+respectively. You shouldn't normally need the index or array to compare values,
+but it's there if you do.
 
 You may also, optionally, specify an input range as the final two parameters,
 in case you want to limit the search to a particular range of inputs. However,