doc: starting draft for v2.6 release notes

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/release_notes/release_notes_2.6.rst

@@ -0,0 +1,65 @@
+.. _release_notes_2.6:
+
+ACRN v2.6 (Sep 2021) - Draft
+############################
+
+We are pleased to announce the release of the Project ACRN hypervisor
+version 2.6.
+
+ACRN is a flexible, lightweight reference hypervisor that is built with
+real-time and safety-criticality in mind. It is optimized to streamline
+embedded development through an open-source platform. See the
+:ref:`introduction` introduction for more information.
+
+All project ACRN source code is maintained in the
+https://github.com/projectacrn/acrn-hypervisor repository and includes
+folders for the ACRN hypervisor, the ACRN device model, tools, and
+documentation. You can either download this source code as a zip or
+tar.gz file (see the `ACRN v2.6 GitHub release page
+<https://github.com/projectacrn/acrn-hypervisor/releases/tag/v2.6>`_) or
+use Git ``clone`` and ``checkout`` commands::
+
+   git clone https://github.com/projectacrn/acrn-hypervisor
+   cd acrn-hypervisor
+   git checkout v2.6
+
+The project's online technical documentation is also tagged to
+correspond with a specific release: generated v2.6 documents can be
+found at https://projectacrn.github.io/2.6/.  Documentation for the
+latest under-development branch is found at
+https://projectacrn.github.io/latest/.
+
+ACRN v2.6 requires Ubuntu 18.04.  Follow the instructions in the
+:ref:`gsg` to get started with ACRN.
+
+
+What's New in v2.6
+******************
+
+Topic
+  Description
+
+
+Upgrading to v2.6 From Previous Releases
+****************************************
+
+We highly recommended that you follow these instructions to
+upgrade to v2.6 from previous ACRN releases.
+
+
+Document Updates
+****************
+
+[Add list of significant doc changes, e.g., new What's ACRN, GSG, Config/Dev
+Intro, ...]
+
+Fixed Issues Details
+********************
+
+.. comment example item
+   - :acrn-issue:`5626` - [CFL][industry] Host Call Trace once detected
+
+
+Known Issues
+************
+