Add a comment which explain why we need to use special function instead of

tr(1)/sed(1)/awk(1).

etc/rc.d/gbde

@@ -18,6 +18,8 @@ start_cmd="gbde_start"
 stop_cmd="gbde_stop"
 
 # Change every ${_src} in ${_str} to ${_dst}.
+# We cannot use tr(1), sed(1) nor awk(1) here, because this script is executed
+# before /usr is mounted.
 local_tr()
 {
 	_str=$1