Upgrade will need Elasticsearch v9

Author: violuke

README.rst

@@ -37,6 +37,8 @@ Features
 The library is compatible with all Elasticsearch versions since 5.x
 **but you have to use a matching major version:**
 
+- For Elasticsearch 9.0 and later, use the major version 9 (9.x.y) of the library.
+
 - For Elasticsearch 8.0 and later, use the major version 8 (8.x.y) of the library.
 
 - For Elasticsearch 7.0 and later, use the major version 7 (7.x.y) of the library.
@@ -45,6 +47,9 @@ The library is compatible with all Elasticsearch versions since 5.x
 
 .. code-block:: python
 
+    # Elasticsearch 9.x
+    elasticsearch-dsl>=9.0.0,<10.0.0
+
     # Elasticsearch 8.x
     elasticsearch-dsl>=8.0.0,<9.0.0