Imo, it's not a good idea to directly link to the extension as one might accidentally hit the "Add to chrome" button. (e.g. when coming from the homepage and not peeking into the thread here)
Edit: well, don't complain about the downvotes, but here I am after a few downvotes thinking "Wow, who are these baby-coddling users who think HN readers are idiots who don't read the headline and just accidentally click 'Add to Chrome'?".