Documentation placeholder for varnishd -l

doc/sphinx/whats-new/upgrading-5.2.rst

@@ -149,6 +149,10 @@ Other changes
 
 * ``varnishd(1)``:
 
+  .. XXX phk, a word on -l changes and the implications on how the
+         working directory may grow in size? This may be a problem
+         when /var/lib/varnish is mounted in RAM.
+
   * The default value of ``server.identity`` when the ``-i`` option is
     not set has been changed as noted above.