docs: added upgrade guide for 1.6.1 (#2561)

docs/content/advanced/backend/upgrade-guides/1-6-1.md

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+---
+description: 'Actions Required for v.1.6.1'
+---
+
+# v1.6.1
+
+Updating your medusa server to version `1.6.1` requires running migrations on your server.
+
+## Overview
+
+As the new version `1.6.1` make changes to the database schema, it is required to run new migrations before you start your server.
+
+Without running the migrations, you might have trouble accessing and using the Medusa admin.
+
+## Actions Required
+
+After updating your server, run migrations with the following command:
+
+```bash
+medusa migrations run
+```