btrbk.conf.example: use @subvol notation

btrbk.conf.example

@@ -144,15 +144,19 @@ volume /mnt/btr_pool
   # Target for all subvolume sections:
   target /mnt/btr_backup/_btrbk
 
-  subvolume  root_gentoo
-  subvolume  kvm
+  # Many default btrfs installations (e.g. Fedora, Ubuntu) prefix the
+  # subvolumes names with "@". Note that this is only a naming
+  # convention.
+  subvolume  @
+  subvolume  @home
+  subvolume  @kvm
     # Use different retention policy for kvm backups:
     target_preserve     7d 4w
 
 
 # Backup data to external disk as well as remote host
 volume /mnt/btr_data
-  subvolume  home
+  subvolume  @data
     # Always create snapshot, even if targets are unreachable
     snapshot_create  always
     target /mnt/btr_backup/_btrbk
@@ -168,10 +172,10 @@ volume ssh://my-remote-host.com/mnt/btr_pool
 
 
 # Resume backups from remote host which runs its own btrbk instance
-# creating snapshots for "home" in "/mnt/btr_pool/btrbk_snapshots".
+# creating snapshots for "@home" in "/mnt/btr_pool/btrbk_snapshots".
 volume ssh://my-remote-host.com/mnt/btr_pool
   snapshot_dir           btrbk_snapshots
   snapshot_create        no
   snapshot_preserve_min  all
-  subvolume home
+  subvolume @home
     target /mnt/btr_backup/_btrbk/my-remote-host.com