help message of btrfsctl does not tell anything about deletion of a subvolume

[Andreas Philipp <philipp.andreas@gmail.com>]

Hi,

The help message of the btrfsctl command does not tell anything about
the deletion of a subvolume. See patch below.

Kind regards,
Andreas

diff --git a/btrfsctl.c b/btrfsctl.c
index be6bf25..3ed6f2d 100644
--- a/btrfsctl.c
+++ b/btrfsctl.c
@@ -56,7 +56,7 @@ static void print_usage(void)
     printf("\t-A device: scans the device file for a Btrfs filesystem\n");
     printf("\t-a: scans all devices for Btrfs filesystems\n");
     printf("\t-c: forces a single FS sync\n");
-    printf("\t-D: delete snapshot\n");
+    printf("\t-D: delete snapshot or subvolume\n");
     printf("\t-m [tree id] directory: set the default mounted subvolume"
            " to the [tree id] or the directory\n");
     printf("%s\n", BTRFS_BUILD_VERSION);