Docs: Add hint to @comet/upgrade (#1637)

docs/docs/migration/index.md

@@ -2,3 +2,21 @@
 title: Migration
 sidebar_position: 12
 ---
+
+This chapter contains instructions for migrating from one COMET DXP version to another.
+
+## @comet/upgrade
+
+Codemods for automated updates, such as renames, are available at [@comet/upgrade](https://github.com/vivid-planet/comet-upgrade).
+
+Example usage for upgrading from v4 to v5 (each major version should be upgraded separately):
+
+```
+npx @comet/upgrade v5
+```
+
+:::caution
+
+Codemods are designed to ensure that upgrades are as smooth as possible, so their use is highly recommended.
+
+:::