I can't really put myself in the shows of someone who'd be triggered by the word trigger, but calling it a content note is sensible.

I wouldn't say I'm easily triggered by anything, but I would have appreciated knowing that the novel I was reading shortly after my dad died of cancer had a plot twist at the end where the lead character died of cancer. I understand not spoiling the plot but I was not in the mood for where that book ended up going! And above everything else it was bloody crap :(