Add a section on WSGI to what's new.

docs/WHATSNEW.rst

@@ -9,6 +9,7 @@ about all minor new features and bugs being solved in this release.
 
 Note: This is currently work-in-progress!
 
+
 Version numbering increase
 --------------------------
 
@@ -23,6 +24,31 @@ version of this project, it was decided to skip ahead and use Zope 4.0 as the
 next version number. The increase in the major part of the version also
 indicates the clear intention to allow backwards incompatible changes.
 
+
+Recommended WSGI setup
+----------------------
+
+Zope 2.13 first gained support for running Zope as a WSGI application,
+using any WSGI capable web server instead of the built-in ZServer.
+
+Zope 4.0 takes this one step further and recommends using WSGI as the
+default setup. In fact ZServer got moved into its own optional project.
+
+If you rely on ZServer features, like Webdav, FTP, zdaemon or zopectl
+support, please make sure to install ZServer and use its ``mkzopeinstance``
+script to create a Zope instance.
+
+By default Zope only ships with a new ``mkwsgiinstance`` script which
+creates a Zope instance configured to run as a WSGI application. The
+example configuration uses the ``waitress`` web server, but Zope can
+be run using any WSGI capable web server.
+
+To make running Zope easier, a new ``runwsgi`` command line script got
+added, which can read a PasteDeploy configuration and create and run
+the WSGI pipeline specified in it. By default such a configuration is
+created in the ``etc/zope.ini`` file.
+
+
 Memory use
 ----------