Expand the HTML 1 tutorial based on confused areas last night.

There were a couple of typos in the HTML 1 tutorial, as well as some parts which tripped up the students I worked with last night. I've cleaned those typos up, added some explanations for confusing bits, removed some
technical language in favour of plain English, and simplified some other sections.
not a big fan of going into comments tbh as they tend to be abused for commenting out code.