liveupdate: document current compatibility status

We currently do not guarantee compatibility due to ongoing
development, so mention this explicitly in the user-facing
documentation.

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://patch.msgid.link/20260527153725.1770394-1-luca.boccassi@gmail.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Author: bluca

Documentation/userspace-api/liveupdate.rst

@@ -14,6 +14,14 @@ ioctl uAPI
 ===========
 .. kernel-doc:: include/uapi/linux/liveupdate.h
 
+Note on Compatibility
+=====================
+
+Note that the Live Update feature is still under development and subject to
+change, so compatibility is not guaranteed when kexec rebooting between
+different kernel versions. This is expected to change and stabilize in a future
+version.
+
 Userspace Integration
 =====================