[DOCS] Adds highlights to the Installation and Upgrade Guide (#252)

Author: lcawl

docs/en/install-upgrade/highlights.asciidoc

@@ -0,0 +1,23 @@
+[[elastic-stack-highlights]]
+== Highlights
+
+This section summarizes the most important enhancements in {version}.
+
+[float]
+[[elasticsearch-highlights]]
+=== {es}
+
+coming[7.0.0]
+
+include::{es-repo-dir}/reference/release-notes/highlights-7.0.0.asciidoc[tag=notable-highlights]
+
+
+[float]
+[[kibana-higlights]]
+=== {kib}
+
+coming[7.0.0]
+
+include::{kib-repo-dir}/release-notes/highlights-7.0.0.asciidoc[tag=notable-highlights]
+
+

docs/en/install-upgrade/index.asciidoc

@@ -13,4 +13,6 @@ include::installing-stack.asciidoc[]
 
 include::upgrading-stack.asciidoc[]
 
-include::breaking.asciidoc[]
+include::highlights.asciidoc[]
+
+include::breaking.asciidoc[]