message: doc: Put PR template in comments
  This prevents the common annoyance of the text being included into PRs
  accidentally.
diff: +<!--
  +*** Please remove the following help text before submitting: ***
  +
  Pull requests without a rationale and clear improvement may be closed
  immediately.
  +-->
  +<!--
  Please provide clear motivation for your patch and explain how it improves
  Bitcoin Core user experience or Bitcoin Core developer experience
  -significantly.
  +significantly:
  * Any test improvements or new tests that improve coverage are always welcome.
  * All other changes should have accompanying unit tests (see `src/test/`) or
  @@ -24,8 +29,11 @@ significantly.
  is often a subjective matter. Unless they are explicitly mentioned to be
  preferred in the [developer notes](/doc/developer-notes.md), stylistic code
  changes are usually rejected.
  +-->
  +<!--
  Bitcoin Core has a thorough review process and even the most trivial change
  needs to pass a lot of eyes and requires non-zero or even substantial time
  effort to review. There is a huge lack of active reviewers on the project, so
  patches often sit for a long time.
  +-->
  