Merge pull request SharePoint#4233 from andrewconnell/docfix-issue4181

Update supported guidance for save site as template

Author: andrewconnell

docs/general-development/save-download-and-upload-a-sharepoint-site-as-a-template.md

@@ -6,6 +6,8 @@ ms.assetid: 2e637172-ddac-4a70-bd77-55a1645a3db1
 localization_priority: Priority
 ---
 
+> [!NOTE]
+> The functionality of saving a site as a template described in this article is **only supported** in SharePoint Server 2013, SharePoint Server 2016, and SharePoint Server 2019 (classic sites only). It is **not supported** & **not supported** in SharePoint Online or SharePoint Server 2019 (modern sites).
 
 # Save, download, and upload a SharePoint site as a template
 Learn how to design and build robust applications by using SharePoint site templates.