fix(migrations): add instructions to bring back custom_migration_cutoff (#2299)

Ref: SRX-C0R01N

Author: AminSlk

docs/rollback.md

@@ -12,3 +12,13 @@ You can easily roll back to an older version of a single service
 ![](../assets/img/rollback/releasedialog-full.png)
 5) Now you have 2 planned actions, that you still need to apply. ![](../assets/img/rollback/planned-actions.png)
 
+# Migrations
+If you've deleted the custom migrations cutoff table and you want to bring it back you can run:
+```Sql
+CREATE TABLE IF NOT EXISTS custom_migration_cutoff
+(
+    migration_done_at TIMESTAMP NOT NULL,
+    kuberpult_version varchar(100) PRIMARY KEY -- the version as it appears on GitHub, e.g. "1.2.3"
+);
+```
+This way you can have this table back.