Fix README typos

[akuhnregnier]

This fixes some minor typos in the documentation.

[casey]

This fixes one type, but introduces a new one.

[akuhnregnier]

That is on purpose, since the sentence where the typo is introduced is meant to illustrate just's ability to catch typos.
At least that's how I understand it. If that's not correct, I will revert that change of course.

[casey]

@akuhnregnier Whoops! Of course you're right. LGTM.

[casey]

Actually, I think that sentence is referring to unwanted space-splitting, not typos. It's a bit unclear though, I'll rewrite it.