link to docker-compose pg13 upgrade instructions

docs/installation-and-operations/misc/migration-to-postgresql13/README.md

@@ -104,6 +104,10 @@ Please follow this section only if you have installed OpenProject using [this pr
 Before attempting the upgrade, please ensure you have performed a backup of your installation by following the [backup guide](../../operation/backing-up/).
 </div>
 
+You can find the upgrade instructions for your docker-compose setup in the [openproject-deploy](https://github.com/opf/openproject-deploy/blob/stable/12/compose/control/README.md#upgrade) repository.
+
+Remember that you need to have checked out that repository and work in the `compose` directory for the instructions to work.
+
 [compose-based-installation]: ../../installation/docker/#one-container-per-process-recommended
 
 ## All-in-one docker installation