docs: release-notes: Add note on Zephyr watchdog changes

Adds release notes for these fixed features

Signed-off-by: Jamie McCrae <[email protected]>

Author: thedjnK

docs/release-notes.d/zephyr-watchdog.md

@@ -0,0 +1,19 @@
+- Watchdog support in Zephyr has been reworked and fixed to allow
+  installing a timeout (with a configurable value) before starting
+  it. The default timeout is set to 1 minute and this feature has
+  been enabled by default. 3 Kconfig options have been added which
+  control how the watchdog is used in MCUboot:
+
+    * ``CONFIG_BOOT_WATCHDOG_SETUP_AT_BOOT`` controls setting up
+      the watchdog in MCUboot (if not set up, it can still be set,
+      if the driver supports this non-compliant behaviour).
+    * ``CONFIG_BOOT_WATCHDOG_INSTALL_TIMEOUT_AT_BOOT`` controls if
+      a timeout is installed at bootup or not.
+    * ``CONFIG_BOOT_WATCHDOG_TIMEOUT_MS`` sets the value of the
+      timeout in ms.
+
+- In addition, Zephyr modules can now over-ride the default
+  watchdog functionality by replacing the weakly defined functions
+  ``mcuboot_watchdog_setup`` and/or ``mcuboot_watchdog_feed``,
+  these functions take no arguments.
+