Added note that ES packages automatically change vm.max_map_count

Closes #8601

docs/reference/setup/configuration.asciidoc

@@ -64,6 +64,8 @@ sysctl -w vm.max_map_count=262144
 To set this value permanently, update the `vm.max_map_count` setting in
 `/etc/sysctl.conf`.
 
+NOTE: If you installed Elasticsearch using a package (.deb, .rpm) this setting will be changed automatically.  To verify, run `sysctl vm.max_map_count`.
+
 [float]
 [[setup-configuration-memory]]
 ==== Memory Settings