doc: update release notes for v2.6 on configuration upgrades

This patch updates recommendations to upgrade from a prior ACRN version for
v2.6.

Signed-off-by: Junjie Mao <junjie.mao@intel.com>

doc/release_notes/release_notes_2.6.rst

@@ -45,6 +45,30 @@ Upgrading to v2.6 From Previous Releases
 We highly recommended that you follow these instructions to
 upgrade to v2.6 from previous ACRN releases.
 
+Generate New Board XML
+======================
+
+Board XML files, generated by ACRN board inspector, contain board information
+that is essential to build ACRN. Compared to previous versions, ACRN v2.6 adds
+the following hardware information to board XMLs to support the new features and
+fixes.
+
+  - Maximum width of physical and linear addresses
+  - Device objects in the ACPI namespace
+  - Routing of PCI interrupt pins
+  - Number of requested vectors of MSI-capable PCI devices
+
+The new board XML can be generated using the ACRN board inspector in the same
+way as ACRN v2.5. Refer to :ref:`acrn_config_workflow` for a complete list of
+steps to deploy and run the tool.
+
+Add New Configuration Options
+=============================
+
+In v2.6, the following elements are added to scenario XML files.
+
+- :option:`hv.FEATURES.ENFORCE_TURNOFF_GP` (Default value is ``n``)
+- :option:`hv.FEATURES.SECURITY_VM_FIXUP` (Default value is ``n``)
 
 Document Updates
 ****************