Add limit filter doc.

docs/Filter/Limit.md

+# Limit Filter
+
+> More info about limit filter is in the [official elasticsearch docs][1]
+
+A limit filter limits the number of documents (per shard) to execute on.
+
+## Simple example
+
+```JSON
+{
+    "filtered" : {
+        "filter" : {
+             "limit" : {"value" : 100}
+         },
+         "query" : {
+            "term" : { "name.first" : "shay" }
+        }
+    }
+}
+```
+
+And now the query via DSL:
+
+```php
+$limitFilter = new LimitFilter(100);
+$termQuery = new TermQuery('name.first', 'shay');
+
+$filteredQuery = new FilteredQuery($termQuery, $limitFilter);
+
+$search = new Search();
+$search->addQuery($filteredQuery);
+$queryArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-limit-filter.html