Improve README

[gilch]

Too vague to really be actionable, I know, but first impressions matter, and I feel like it could be better than it is.

GitHub markdown is pretty limiting. Most interactivity is not allowed. Animated GIFs are possible, and I'm considering adding some. It does grab one's attention, and can show things off without too much effort from the watcher. I could probably put the whole quickstart[whirlwind tour] in there with one GIF per section. But making them is a significant effort and the docs are still in flux. There's probably a way to automate this, but I might have to write most of that myself.

I could also possibly link them to a "static" page that loads a Lissp REPL via pyodide. It's kind of slow loading on the first try though. And it would be a nontrivial effort to get it working. I've considered using Brython in the docs, but it had bugs at the time. That would at least load faster, but probably also a nontrival effort.

Hissp keeps gradually accumulating stars, but so far, not many users are doing anything visible with it. I'm considering adding social media buttons to the top of the readme, but since I try not to use those myself, they might be hard for me to test.

[gilch]

Hissp 0.3.0 installs in pyodide now that it has a wheel on PyPI. Haven't tried Brython lately.

[gilch]

Some progress on this in #164.