Document changes to varnishlog and varnishstat regarding hit-for-miss/-pass

in What's New for 5.1.

doc/sphinx/whats-new/upgrading-5.1.rst

@@ -12,3 +12,14 @@ vcl_backend_response
 
 * Added ``return(pass(DURATION))`` to set an object to hit-for-pass,
   see :ref:`whatsnew_changes_5.1_hitpass`.
+
+Other changes
+=============
+
+* Added the ``cache_hitmiss`` stat to ``varnishstat(1)`` to count hits on
+  hit-for-miss objects.
+
+* The ``cache_hitpass`` stat now only counts hits on hit-for-pass objects.
+
+* An entry with the ``TTL`` tag and the prefix ``HFP`` is logged in
+  ``varnishlog(1)`` to record the duration set for hit-for-pass objects.