prettify/edit and convert introduction into markdown

In working on this I realized I'm a little confused about what the objective is in converting this to markdown. Are we simply taking the bulleted list you pulled from the workflowy and making it prettier using markdown (what I did here)? Or are we expanding the bulleted list into more of a paragraph format so that someone who is not receiving the actual insruction/lecture part of codefellows could follow along?

I mostly just converted the bullets to headings here, fixed a few typos, and reworded a couple things to make them clearer. I also made the links prettier. I didn't want to spend the time paragraph-ifying it if that was not actually the goal, but it would be pretty easy to do.

Before we get too much further we might want to have some sort of style guide for what size headings get used where and whatnot so that we're all doing things the same way. I am not at all attached to the way I did it, I just kind of did whatever looked nicest to me, but we can discuss other ways too.

Also, I found a couple broken links that I marked with (THIS LINK IS BROKEN) and put in some other all caps comments in places I though could use more clarification in the setup section (which is likely in the slides, but I don't know where those are).