doc/next: add small header to TODO

Change-Id: I91c03f455fff8e4078f3297ea357cd1e1dd09f66
Reviewed-on: https://go-review.googlesource.com/c/go/+/676536
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: dr2chase

doc/next/9-todo.md

@@ -1,6 +1,10 @@
 <!--
 Output from relnote todo that was generated and reviewed on 2025-05-23, plus summary info from bug/CL: -->
 
+### TODO
+
+**Please turn these into proper release notes**
+
 <!-- TODO: CL 420114 has a RELNOTE comment without a suggested text (from RELNOTE comment in https://go.dev/cl/420114) -->
 all: implement plugin build mode for riscv64