adding 7.x to docs

Author: honzakral

docs/index.rst

@@ -30,6 +30,9 @@ Compatibility
 The library is compatible with all Elasticsearch versions since ``2.x`` but you
 **have to use a matching major version**:
 
+For **Elasticsearch 6.0** and later, use the major version 7 (``7.x.y``) of the
+library.
+
 For **Elasticsearch 6.0** and later, use the major version 6 (``6.x.y``) of the
 library.
 
@@ -42,6 +45,9 @@ library.
 The recommended way to set your requirements in your `setup.py` or
 `requirements.txt` is::
 
+    # Elasticsearch 7.x
+    elasticsearch-dsl>=7.0.0,<8.0.0
+
     # Elasticsearch 6.x
     elasticsearch-dsl>=6.0.0,<7.0.0