Update README.md

Author: sensuikan1973

elasticsearch-model/README.md

@@ -16,6 +16,7 @@ The version numbers follow the Elasticsearch major versions. Currently the `main
 | 2.x           | → | 2.x           |
 | 5.x           | → | 5.x           |
 | 6.x           | → | 6.x           |
+| 7.x           | → | 7.x           |
 | main          | → | 7.x           |
 
 ## Installation