[DOCS] Added link to product compatibility matrix
Original commit: elastic/x-pack-elasticsearch@08d83fee6c87a1d43c168cd562ceb83f8ddcdd34
@@ -9,7 +9,10 @@ After you install {es}, you can optionally obtain and install {xpack}.
For more information about how to obtain {xpack},
see https://www.elastic.co/products/x-pack.
-You must run the version of {xpack} that matches the version of {es} you are running.
+You must run the version of {xpack} that matches the version of {es} you are
+running. See the
+https://www.elastic.co/support/matrix#matrix_compatibility[Elastic Support Matrix]
+for more information about product compatibility.
IMPORTANT: If you are installing {xpack} for the first time on an existing
cluster, you must perform a full cluster restart. Installing {xpack} enables
