add upgrade

docs/en/docs/pro/upgrade.md

@@ -0,0 +1,17 @@
+# Upgrade from the open source version
+
+It's so easy to upgrade `fastapi-admin` open source version to pro version, because pro version contains all of open source and has same project structure.
+
+1. Uninstall open source version.
+
+    ```shell
+    > pip uninstall fastapi-admin
+    ```
+
+2. Install pro version.
+
+    ```shell
+    > pip install git+https://${GH_TOKEN}@github.com/fastapi-admin/fastapi-admin-pro.git
+    ```
+
+That's all, then you can add pro version exclusive content yourself without any code change.

docs/en/mkdocs.yml

@@ -68,6 +68,7 @@ nav:
       - pro/sponsor.md
       - pro/exclusive.md
       - pro/installation.md
+      - pro/upgrade.md
       - pro/support.md
 extra:
   alternate: