docs(filterFilter): add note on negation

Author: guilbep

src/ng/filter/filter.js

@@ -23,7 +23,9 @@
  *     which have property `name` containing "M" and property `phone` containing "1". A special
  *     property name `$` can be used (as in `{$:"text"}`) to accept a match against any
  *     property of the object. That's equivalent to the simple substring match with a `string`
- *     as described above.
+ *     as described above. The predicate can be negated by prefixing the string with `!`.
+ *     For Example `{name: "!M"}` predicate will return an array of items which have property `name`
+ *     not containing "M".
  *
  *   - `function(value, index)`: A predicate function can be used to write arbitrary filters. The
  *     function is called for each element of `array`. The final result is an array of those