docs(): updated export docs

docs/sources/reference/export_import.md

@@ -14,6 +14,14 @@ The export feature is accessed from the share menu.
 
 <img src="/img/v31/export_menu.png">
 
+### Making a dashboard portable
+
+If you want to export a dashboard for others to use then it could be a good idea to
+add template variables for things like a metric prefix (use contant variable) and server name.
+
+A template varible of the type `Constant` will automatically be hidden in
+the dashboard, and will also be added as an required input when the dashboard is imported.
+
 ## Importing a dashboard
 
 To import a dasbhoard open dashboard search and then hit the import button.