Add more like this query doc.

docs/Query/MoreLikeThis.md

+# More Like This Query
+
+> More info about more like this query is in the [official elasticsearch docs][1]
+
+The More Like This Query (MLT Query) finds documents that are "like" a given set of documents.
+
+## Simple example
+
+```JSON
+{
+    "more_like_this" : {
+        "fields" : ["title", "description"],
+        "like_text" : "Once upon a time",
+        "min_term_freq" : 1,
+        "max_query_terms" : 12
+    }
+}
+```
+
+In DSL:
+
+```php
+$moreLikeThisQuery = new MoreLikeThisQuery(
+    'Once upon a time',
+    [
+        'fields' => ['title', 'description'],
+        'min_term_freq' => 1,
+        'max_query_terms' => 12,
+    ]
+);
+
+$search = new Search();
+$search->addQuery($moreLikeThisQuery);
+
+$queryArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-mlt-query.html