[FIX] Advanced Chart should be more explicit for new users ( I still have some...

[FIX] Advanced Chart should be more explicit for new users ( I still have some modifications to add).

templates/chart.html

@@ -247,7 +247,7 @@
                                     <input ng-if="filter.operator" type="text" ng-model="filter.value" ng-change="updateQuery()">
                                 </span>
                                 <span ng-if="filter.entity.key == 'ngrams'">
-                                    are in this list:
+                                    are in this list of words or expressions:
                                     <tags-input ng-model="filter.value" display-property="terms" placeholder="Add an ngram" on-tag-added="updateQuery()" on-tag-removed="updateQuery()" add-from-autocomplete-only="true">
                                         <auto-complete source="getNgrams($query)"></auto-complete>
                                     </tags-input ng-model="tags">