Start the skeleton release notes for release 6.0.

Just full of XXX's for now.

doc/sphinx/whats-new/changes-6.0.rst

+.. _whatsnew_changes_6.0:
+
+Changes in Varnish 6.0
+======================
+
+XXX: ... intro paragraphs ...
+
+.. _whatsnew_new_subhead_1:
+
+XXX subhead 1
+~~~~~~~~~~~~~
+
+XXX ...
+
+XXX subsubhead 1.1
+------------------
+
+XXX: ...
+
+XXX subsubhead 1.2
+------------------
+
+XXX: ...
+
+XXX subhead 2
+~~~~~~~~~~~~~
+
+XXX ...
+
+XXX subsubhead 2.1
+------------------
+
+XXX: ...
+
+News for authors of VMODs and Varnish API client applications
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. _whatsnew_dev_subhead_1:
+
+XXX dev subhead 1
+-----------------
+
+XXX ...
+
+.. _whatsnew_dev_subhead_2:
+
+XXX dev subhead 2
+-----------------
+
+XXX ...
+
+*eof*

doc/sphinx/whats-new/index.rst

@@ -8,6 +8,15 @@ This section describes the changes and improvements between different
 versions of Varnish, and what upgrading between the different versions
 entail.
 
+Varnish 6.0
+-----------
+
+.. toctree::
+   :maxdepth: 2
+
+   changes-6.0
+   upgrading-6.0
+
 Varnish 5.2
 -----------
 

doc/sphinx/whats-new/upgrading-6.0.rst

+.. _whatsnew_upgrading_6.0:
+
+%%%%%%%%%%%%%%%%%%%%%%%%
+Upgrading to Varnish 6.0
+%%%%%%%%%%%%%%%%%%%%%%%%
+
+XXX: Most important change first
+================================
+
+XXX ...
+
+varnishd parameters
+===================
+
+XXX: ... terse overview, use refs to link to details ...
+
+Changes to VCL
+==============
+
+XXX: ... intro paragraph
+
+XXX VCL subhead 1
+~~~~~~~~~~~~~~~~~
+
+XXX: ... etc.
+
+VCL variables
+~~~~~~~~~~~~~
+
+XXX: VCL vars subhead 1
+-----------------------
+
+XXX: ...
+
+XXX: VCL vars subhead 2
+-----------------------
+
+XXX: ...
+
+XXX VCL subhead 2
+~~~~~~~~~~~~~~~~~
+
+XXX: ...
+
+Other changes
+=============
+
+* ``varnishd(1)``:
+
+  * XXX ...
+
+  * XXX ...
+
+* ``varnishstat(1)``:
+
+  * XXX ...
+
+  * XXX ...
+
+* XXX: etc. ...
+
+  * XXX ...
+
+  * XXX ...
+
+* Changes for developers:
+
+  * XXX ...
+
+  * XXX ...
+
+*eof*