There's a new inline comment help. That's great. It also explains who will be notified of comments. That's great too. But the wording doesn't clearly exclude a common newbie mistake: it's not apparent that only one person can be @notified. Here's a proposed improvement:
Comments use mini-Markdown formatting:
[link](http://example.com) _italic_ **bold** `code`. The post author will automatically be notified of your comment. To notify a previous commenter (just one), mention their user name:
@PeterSmith will both work.
(Added “(just one)”)