Updating migration guide

- added: short, concise mention of the alternative migration method using the backup_and_restore script
- changed: made it clear in the Warning on step 3 that this affects the target machine, not the source machine

docs/i_u_m_migration.md

@@ -1,5 +1,7 @@
 #### Please note: This guide assumes you intend to migrate an existing mailcow server (source) over to a brand new, empty server (target). It takes no care about preserving any existing data on your target server and will erase anything within `/var/lib/docker/volumes` and thus any Docker volumes you may have already set up.
 
+##### Alternatively, you can use the `./helper-scripts/backup_and_restore.sh` script to create a full backup on the source machine, then install Mailcow on the target machine as usual, copy over your `mailcow.conf` and use the same script to restore your backup to the target machine.
+
 **1\.** 
 Install [Docker](https://docs.docker.com/engine/installation/linux/) and [Docker Compose](https://docs.docker.com/compose/install/) on your new server.
 
@@ -25,10 +27,10 @@ Please use the latest Docker engine available and do not use the engine that shi
 systemctl status docker.service
 ```
     
-**3\.**	Run the following commands on the source machine (take care of adding the trailing slashes in the first path parameter as shown below!) - **WARNING: This command will erase anything that may already exist under `/var/lib/docker/volumes`**:
+**3\.**	Run the following commands on the source machine (take care of adding the trailing slashes in the first path parameter as shown below!) - **WARNING: This command will erase anything that may already exist under `/var/lib/docker/volumes` on the target machine**:
 ```
-rsync -aHhP --numeric-ids --delete /opt/mailcow-dockerized/ root@some.other.machine.net:/opt/mailcow-dockerized
+rsync -aHhP --numeric-ids --delete /opt/mailcow-dockerized/ root@target-machine.example.com:/opt/mailcow-dockerized
-rsync -aHhP --numeric-ids --delete /var/lib/docker/volumes/ root@some.other.machine.net:/var/lib/docker/volumes
+rsync -aHhP --numeric-ids --delete /var/lib/docker/volumes/ root@target-machine.example.com:/var/lib/docker/volumes
 ```
 
 **4\.** Shut down mailcow and stop Docker on the source machine.