doc: release-notes-3.7: add Task Watchdog section

Mention the newly added shell for the task watchdog subsystem.

Signed-off-by: Martin Jäger <martin@libre.solar>

Author: martinjaeger

doc/releases/release-notes-3.7.rst

@@ -1814,6 +1814,10 @@ Libraries / Subsystems
 
   * Fixed FAT driver leaving disk in initialized state after unmount.
 
+* Task Watchdog
+
+  * Added shell (mainly for testing purposes during development).
+
 * POSIX API
 
   * Improved Kconfig options to reflect standard POSIX Options and Option Groups.