Add what's new for 3.9

doc/htmldoc/whats_new/index.rst

@@ -8,6 +8,7 @@ versions of NEST. On the linked pages, you will find both information about new
 features, as well as quick guides on how to transition your simulation code to
 the new versions.
 
+* :ref:`NEST 3.9 <release_3.9>`
 * :ref:`NEST 3.8 <release_3.8>`
 * :ref:`NEST 3.7 <release_3.7>`
 * :ref:`NEST 3.6 <release_3.6>`
@@ -23,6 +24,7 @@ the new versions.
    :hidden:
    :glob:
 
+   v3.9/*
    v3.8/*
    v3.7/*
    v3.6/*

doc/htmldoc/whats_new/v3.9/index.rst

@@ -0,0 +1,41 @@
+.. _release_3.9:
+
+What's new in NEST 3.9
+======================
+
+This page contains a summary of important breaking and non-breaking
+changes from NEST 3.8 to NEST 3.9.
+
+If you transition from an earlier version, please see our extensive
+:ref:`transition guide from NEST 2.x to 3.0 <refguide_2_3>` and the
+:ref:`list of updates for previous releases in the 3.x series <whats_new>`.
+
+
+The release of 3.9 brought a lot of changes with 110 PRs
+including 19 bug fixes and 10 enhancements as detailed in the `release notes
+on GitHub <https://github.com/nest/nest-simulator/releases/>`_. Here are some
+of the more interesting developments that happened:
+
+
+Model improvements
+------------------
+
+* Biologically-inspired features added to e-prop plasticity
+
+  See :doc:`/auto_examples/eprop_plasticity/index`
+
+* The tripartite connectivity, used for Astrocytes, now supports multiple primary
+  connection rules.
+
+  See :doc:`Astrocyte examples </auto_examples/astrocytes/index>`
+
+Documentation additions
+-----------------------
+
+* We now have a detailed description of neuron models in NEST, inclduding :ref:`update
+  algorithm <neuron_update>` and :ref:`neuron types <types_neurons>`.
+
+* We updated the :ref:`Built-in timers <built_in_timers>` section to include a graphical description of a simulation run
+  focusing on timers.
+
+* For Windows users, we added a :ref:`helpful guide <windows_install>` to get NEST running on that platform with Docker.