Update whatsnew for v3.3.0rc0 (#4921)

* update whatsnew

* fix index

* remove template

* address review comments

Author: stephenworsley

docs/src/whatsnew/latest.rst renamed to docs/src/whatsnew/3.3.rst

@@ -1,13 +1,13 @@
 .. include:: ../common_links.inc
 
-|iris_version| |build_date| [unreleased]
-****************************************
+v3.3 (18 Aug 2022) [release candidate]
+**************************************
 
 This document explains the changes made to Iris for this release
 (:doc:`View all changes <index>`.)
 
 
-.. dropdown:: :opticon:`report` |iris_version| Release Highlights
+.. dropdown:: :opticon:`report` v3.3.0 Release Highlights
    :container: + shadow
    :title: text-primary text-center font-weight-bold
    :body: bg-light
@@ -16,7 +16,16 @@ This document explains the changes made to Iris for this release
 
    The highlights for this minor release of Iris include:
 
-   * N/A
+   * We've added support for datums, loading them from NetCDF when the
+     :obj:`iris.FUTURE.datum_support` flag is set.
+   * We've greatly improved the speed of linear interpolation.
+   * We've added the function :func:`iris.pandas.as_cubes` for richer
+     conversion from Pandas.
+   * We've improved the functionality of :func:`iris.util.mask_cube`.
+   * We've improved the functionality and performance of the
+     :obj:`iris.analysis.PERCENTILE` aggregator.
+   * We've completed implementation of our :ref:`contributing.benchmarks`
+     infrastructure.
 
    And finally, get in touch with us on :issue:`GitHub<new/choose>` if you have
    any issues or feature requests for improving Iris. Enjoy!

docs/src/whatsnew/index.rst

@@ -5,13 +5,13 @@
 What's New in Iris
 ------------------
 
-.. include:: latest.rst
+.. include:: 3.3.rst
 
 .. toctree::
    :maxdepth: 1
    :hidden:
 
-   latest.rst
+   3.3.rst
    3.2.rst
    3.1.rst
    3.0.rst