Clarify issue/PR choreography

From a discussion with @picnixz:

I think the problem with the devguide is the first sentence is "Create an issue that describes the change" and you'll see the mention to DPO only during creation. We can improve that
I would expect people to read the issue template correctly and understand that something is not trivial
and more importantly: WAIT for triagers to decide whether it's ok or not as an issue
There are obvious cases where the issue doesn't a triager for validation, like a clear bug (and even this is subject to interpretation sometimes) but the process issue+PR is the worst for triagers, especially when the PR is automated.

This might be a duplicate of other feedback here in issues, but I wanted to capture it before going back to $WORK.

まず devguide の冒頭の手順と issue template の場所を確認し、次に DPO と triager に関するガイダンスがどこで導入されているかを確認します。Contributor は PR を開く前に triager による検証を待つべきであることを明確にしつつ、明確なバグをめぐる議論にも触れます。issue-to-PR ワークフローと例外が contributor にとって明示的になっていれば完了です。