doc: releases: Add migration notes for v2.0.0

Adding content into a placeholder migration notes for v2.0.0 release.

Signed-off-by: Tommi Rantanen <tommi.rantanen@nordicsemi.no>

Author: trantanen

doc/releases/migration_notes_v2.0.0.rst

@@ -15,4 +15,14 @@ Required changes
 
 The following changes are mandatory to make your application work in the same way as in previous releases.
 
-No changes since the latest release.
+* Full FOTA - When compiling, rename ``overlay-full_fota.conf`` to ``overlay-full-fota.conf`` and add ``PM_STATIC_YML_FILE=pm_static_nrf9151dk_nrf9151_ns_full_fota.yml`` to the build configuration.
+  See :ref:`SM_AT_FOTA` for more information.
+
+Informational changes
+*********************
+
+The following changes are listed for informational purposes, and many hosts will work without any changes.
+
+* Ring Indication (RI) - Change RI from pulse (100 ms) to level triggered, meaning RI stays asserted until the host asserts DTR.
+  After the Serial Modem has enabled UART, RI will be deasserted.
+* nRF Cloud transport has been changed from MQTT to CoAP.