Add suboption help texts

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/parse.h b/parse.h
index 1a71864..752da34 100644
--- a/parse.h
+++ b/parse.h
@@ -22,6 +22,7 @@
 struct value_pair {
 	const char *ival;		/* string option */
 	unsigned int oval;		/* output value */
+	const char *help;		/* help text for sub option */
 };
 
 #define PARSE_MAX_VP	16