documentation

Author: faissaloux

Diff for: README.md

@@ -60,3 +60,9 @@ This plugin afford math related expectations.
     expect(6)->toBeFactorialOf(3);
     expect(4)->not->toBeFactorialOf(2);
 ```
+
+#### `toBeMaxOf()`
+```php
+    expect(6)->toBeMaxOf([-6, 0, 6]);
+    expect(5.5)->not->toBeMaxOf([2, 4.2, 5.5, 6]);
+```