Touch up various pages’ text

On all changed pages:

- “smarten” apostrophes – change ' to ’

On “About”:

- Fix the capitalization of the names of the three technologies this site uses, and make them all links in case people haven’t heard of them before.
- Move the `<dl>` out of the `<p>`. According to https://developer.mozilla.org/en-US/docs/Web/HTML/Element/p, `<p>` should only contain phrasing content, not flow content. This does not change the visuals.
- To keep the “FAQ:” still related to the following questions and answers, make it a header. An `<h3>` rather than an `<h2>` just because the `<h2>` looks too big, and I don’t want to bother writing a custom style for it. Following an `<h1>` by an `<h3>` may be a bit weird semantically, but at least it’s better than the `<p>` it was before.

On “How to Sign Up”:

- make the sentence grammatical by adding “or”
- capitalize “GitHub” properly

I also added my username to the authorized user list.