It took me ages to find the excellent and comprehensive help for Markdown at https://meta.stackoverflow.com/editing-help. It's not in the SO faq, and it's referenced in very few of the questions tagged faq here. I was sure there should be such a page, but had to dig hard.
Reasons I think it's a good idea:
It's a clear and obvious place to put a link, even if there are other ways. It wouldn't take long. Why not just pop one in?
People used to Windows expect a tooltip from a
?button, so are conditioned to ignore it, and certainly wouldn't think to go there for detail. (Maybe also rename the
?feature, which is excellent, to
More Markdown helpor
Using Markdownto sell it better.)
After you've typed a bit, the helpful "How to Edit"/"How to Format" sidebar turns into "Similar Questions", so if you only need help with markup a little later into posting, most of the help has disappeared, so you look in the faq.
I write all my long posts, and some of my short ones in a text editor (with a compiler or interpreter at the ready), so there's no context-sensitive help most of the time, so I head for the faq.
The link at the bottom of "How to Format" is not visible on a short post on lower screen resolutions (eg. on an ultra portable), so if I want more detail, I look in the faq.
If you're using SO from a mobile device, no help appears at all, for obvious reasons of screen size - I'd still expect to be able to find help in the faq or help, though.
Wouldn't it be an easy edit with a win for some newcomers? If there are other help pages like https://meta.stackoverflow.com/editing-help, it would be nice to like to them or a summary page too. Also, perhaps a link to the well organised main SE faq question, which isn't always at the top of the list, would be better than just linking to the
[faq] tag on meta.