Add not filter doc.

docs/Filter/Not.md

+# Not Filter
+
+> More info about not filter is in the [official elasticsearch docs][1]
+
+A filter that filters out matched documents using a query.
+
+## Simple example
+
+```JSON
+{
+    "filtered" : {
+        "query" : {
+            "term" : { "name.first" : "shay" }
+        },
+        "filter" : {
+            "not" : {
+                "range" : {
+                    "postDate" : {
+                        "from" : "2010-03-01",
+                        "to" : "2010-04-01"
+                    }
+                }
+            }
+        }
+    }
+}
+```
+
+And now the query via DSL:
+
+```php
+$rangeFilter = new RangeFilter(
+    'postDate',
+    [
+        'from' => '2010-03-01',
+        'to' => '2010-04-01',
+    ]
+);
+
+$notFilter = new NotFilter($rangeFilter);
+
+$termQuery = new TermQuery('name.first', 'shay');
+$filteredQuery = new FilteredQuery($termQuery, $notFilter);
+
+$search = new Search();
+$search->addQuery($filteredQuery);
+$queryArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-not-filter.html