templates: mark tumbleweed broken (issue 1496)

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

examples/experimental/opensuse-tumbleweed.yaml

@@ -1,3 +1,6 @@
+# NOTE: Tumbleweed image is known to be broken as of April 2023:
+# https://github.com/lima-vm/lima/issues/1496
+#
 # This example requires Lima v0.11.3 or later
 images:
 # Hint: run `limactl prune` to invalidate the "Current" cache