Rename importing to legacy upgrade

Author: nabeelio

docs/installation/importing.md renamed to docs/installation/legacy-upgrade.md

@@ -1,6 +1,6 @@
 ---
-id: importing
-title: Importing
+id: legacy-upgrade
+title: Upgrading from 5.x
 ---
 You can import through either the installer or the command line after install.
 

sidebars.js

@@ -18,8 +18,8 @@ module.exports = {
         'installation/uploading',
         'installation/vhost',
         'installation/installation',
+        'installation/legacy-upgrade',
         'installation/cron',
-        'installation/importing',
         'installation/updating',
         'installation/docker',
         'installation/issues',