docs(autocomplete): Add missing documentation

src/auto-complete.js

@@ -27,6 +27,10 @@
  *    gains focus. The current input value is available as $query.
  * @param {boolean=} [selectFirstMatch=true] Flag indicating that the first match will be automatically selected once
  *    the suggestion list is shown.
+ * @param {expression=} [matchClass=NA] Expression to evaluate for each match in order to get the CSS classes to be used.
+ *    The expression is provided with the current match as $match, its index as $index and its state as $selected. The result
+ *    of the evaluation must be one of the values supported by the ngClass directive (either a string, an array or an object).
+ *    See https://docs.angularjs.org/api/ng/directive/ngClass for more information.
  */
 tagsInput.directive('autoComplete', function($document, $timeout, $sce, $q, tagsInputConfig, tiUtil) {
     function SuggestionList(loadFn, options, events) {