Add match all query doc.

docs/Query/MatchAll.md

+# Match All Query
+
+> More info about match all query is in the [official elasticsearch docs][1]
+
+A query that matches all documents
+
+## Simple example
+
+```JSON
+{
+    "match_all" : { }
+}
+```
+
+In DSL:
+
+```php
+$matchAllQuery = new MatchAllQuery();
+
+$search = new Search();
+$search->addQuery($matchAllQuery);
+
+$queryArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-match-all-query.html