Missing parameter in comment

Change-Id: Iba55013b3be00974321ad58a276bb37ff2cac4da
diff --git a/lib/lvm b/lib/lvm
index 99c7ba9..0cebd92 100644
--- a/lib/lvm
+++ b/lib/lvm
@@ -101,7 +101,7 @@
 # init_lvm_volume_group() initializes the volume group creating the backing
 # file if necessary
 #
-# Usage: init_lvm_volume_group() $vg
+# Usage: init_lvm_volume_group() $vg $size
 function init_lvm_volume_group {
     local vg=$1
     local size=$2