Add What's New section for 3.8 in docs

doc/htmldoc/whats_new/v3.8/index.rst

@@ -0,0 +1,46 @@
+.. _release_3.8:
+
+What's new in NEST 3.8
+======================
+
+This page contains a summary of important breaking and non-breaking
+changes from NEST 3.7 to NEST 3.8. In addition to the `release notes
+on GitHub <https://github.com/nest/nest-simulator/releases/>`_, this
+page also contains transition information that helps you to update
+your simulation scripts when you come from an older version of NEST.
+
+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>`.
+
+
+NMDA dynamics after Brunel and Wang (2001)
+------------------------------------------
+
+A new integrate-and-fire model allows for the use
+simplified NMDA dynamics.
+It contains exponential conductance-based AMPA and GABA synapses along with NMDA synapses
+weighted such that it approximates the original linear dynamics.
+
+For futher information see:
+
+* :doc:`/auto_examples/wang_decision_making`
+* :doc:`/models/iaf_bw_2001`
+* :doc:`/models/iaf_bw_2001_exact`
+
+New "How NEST works" diagram for docs
+-------------------------------------
+
+The main page of the docs now contains a diagram highlighting the
+fundamental components of creating network simulations in NEST.
+
+* :doc:`/index`
+
+
+NEST performance benchmarks
+---------------------------
+
+You can now view results of this release in benchmarks of
+strong and weak scaling at various network sizes in our docs.
+
+* :ref:`nest_benchmark_results`