Update varnish.rst

Author: gonzalovilaseca

cookbook/cache/varnish.rst

@@ -57,7 +57,8 @@ Symfony2 adds automatically:
             // For Varnish < 3.0
             // esi;
         }
-        /* Do not cache if no-cache is found in headers */
+        /* By default Varnish ignores Cache-Control: nocache (https://www.varnish-cache.org/docs/3.0/tutorial/increasing_your_hitrate.html#cache-control),
+        so in order avoid caching it has to be done explicitly */
         if (beresp.http.Pragma ~ "no-cache" ||
              beresp.http.Cache-Control ~ "no-cache" ||
              beresp.http.Cache-Control ~ "private") {