boards: thingy52: add vendor note on support status

Nordic Semiconductor no longer offers support for this board, so warn
users to avoid it for new prototypes.

(cherry picked from commit 06d2d4e)

Original-Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
GitOrigin-RevId: 06d2d4e
Change-Id: I449c87684d165a22f5239eb40dc95bde202d0906
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5356061
Reviewed-by: Tristan Honscheid <honscheid@google.com>
Commit-Queue: Tristan Honscheid <honscheid@google.com>
Tested-by: Tristan Honscheid <honscheid@google.com>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>

boards/nordic/thingy52/doc/index.rst

@@ -3,6 +3,11 @@
 Thingy:52
 #########
 
+.. warning::
+
+ Nordic Semiconductor no longer offers support for this board, so it is not
+ recommended for new prototypes.
+
 Overview
 ********