siint range parsing HOWTO update

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index a2070d6..c8a84ae 100644
--- a/HOWTO
+++ b/HOWTO
@@ -176,6 +176,8 @@
 	meaning kilo, mega, and giga. So if you want to specify 4096,
 	you could either write out '4096' or just give 4k. The postfixes
 	signify base 2 values, so 1024 is 1k and 1024k is 1m and so on.
+	If the option accepts an upper and lower range, use a colon ':'
+	or minus '-' to seperate such values. See irange.
 bool	Boolean. Usually parsed as an integer, however only defined for
 	true and false (1 and 0).
 irange	Integer range with postfix. Allows value range to be given, such