Correct the description of the second and third fields.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1066 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishstat/varnishstat.1

@@ -38,9 +38,9 @@ The columns in the main display are, from left to right:
 .It
 Total since startup
 .It
-Delta since last update
+Per-second average in the period since last update
 .It
-Average over process lifetime
+Per-second average over process lifetime
 .It
 Descriptive text
 .El