Upgrading MSI installation (#1467)

* Upgrading MSI installation

* Update docs/en/ingest-management/elastic-agent/install-agent-msi.asciidoc

---------

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>
(cherry picked from commit 7ce9dd0)

docs/en/ingest-management/elastic-agent/install-agent-msi.asciidoc

@@ -47,7 +47,7 @@ Installing using an MSI package has the following behaviors:
 [discrete]
 == Upgrading
 
-The {agent} version can be upgraded via {fleet}, but the registered MSI version will display the initially installed version. Attempts to upgrade outside of {fleet} via the MSI will require an uninstall and reinstall procedure to upgrade. 
+The {agent} version can be upgraded via {fleet}, but the registered MSI version will display the initially installed version (this shortcoming will be addressed in future releases). Attempts to upgrade outside of {fleet} via the MSI will require an uninstall and reinstall procedure to upgrade. Also note that this MSI implementation relies on the tar {agent} binary to upgrade the installation. Therefore if the {agent} is installed in an air-gapped environment, you must ensure that the tar image is available before an upgrade request is issued. 
 
 [discrete]
 == Installing in a custom location