[backup] update module descriptions

machines/modules/malobeo/backup.nix

@@ -35,13 +35,22 @@ in
         options = {
           sourceDataset = mkOption {
             type = types.str;
+            description = "The source that needs to be backed up";
           };
           targetDataset = mkOption {
             type = types.str;
+            description = "The target dataset where the backup should be stored";
           };
         };
       })));
-      description = "Hostname with list of datasets to backup.";
+      description = '''
+          Hostname with list of datasets to backup. This option should be defined on hosts that will store backups.
+
+          It is necessary to add the machines that get backed up to known hosts.
+          This can be done for example systemwide using 
+          programs.ssh.knownHosts."10.100.0.101" = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHqp2/YiiIhai7wyScGZJ20gtrzY+lp4N/8unyRs4qhc";
+          Or set it for the syncoid user directly.
+        ''';
     };
 
     sshKey = mkOption {