avoid comment in multi-line command

unit-files/backup@.service

@@ -27,6 +27,6 @@ ExecStart=/bin/bash -euxc ' \
   git config --local user.email "backups@%i"; \
   git config --local user.name "backup service running at %i"; \
   git commit --allow-empty -m"backup %i @ `hostname` - `date`"; \
-  # be careful: hidden sync functionnality; \
+  echo "be careful: hidden sync functionnality"; \
   git pull --rebase; \
   git push origin master'