HTML5 isn't that different from HTML. For a great resource, check out Apple's developer site. Here's the section on Safari: http://developer.apple.com/safari/.
In terms of what editor you should use: You can use whatever editor you want! Notepad for Windows works fine ;) On the Mac, I prefer Coda or Textwranger. Dashcode will work too! In order to write HTML5, you just need to know HTML, CSS and Javascript (jQuery would help too).
And, what's more, since this is just HTML, don't forget you can test it in the browser on your desktop before you test on the iPhone or the iPhone Simulator (included in Xcode). I'd recommend testing in Safari first and Google Chrome second.
Good luck and welcome to the wonderful world of HTML5 and iPhone development!