tweak MD5 config text

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/Config.in b/libbb/Config.in
index 9b616d1..bdb6dfa 100644
--- a/libbb/Config.in
+++ b/libbb/Config.in
@@ -13,7 +13,7 @@
 	  Minimum allowable password length.
 
 config MD5_SIZE_VS_SPEED
-	int "MD5: Trade Bytes for Speed"
+	int "MD5: Trade bytes for speed (0:fast, 3:slow)"
 	default 2
 	range 0 3
 	help