Minor typography fixes

[toastal]

Most of the README uses typographic apostrophes (aka “curly”). This
commit fixes that one non-matching one. It also turns the -- into a
proper em dash — as Markdown unlike AsciiDoc doesn’t support this
transformation by default.

[thomashoneyman]

I think any incidence of a curly apostrophe is a mistake — I'd rather use normal ASCII, ie. '. Do you mind switching to that instead of the curly? Thanks for your recent fixup commits in this repo!

[toastal]

I do not mind helping. It’s certainly your call. However, typographically the ’ is more correct as the ' is a legacy thing with typewriters. Personally I feel it’s all arbitrary on what’s considered ‘easy to type’ as UK keyboards have issue with apply because $).

If you want your README to look ‘beautiful’ while maintaining ease of typing, AsciiDoc does text replacements. Bonuses include, proper titles for code blocks, no need to manually number ordered lists, admonitions (using a blockquote with > for “Alternately, …” is the wrong element).