Fix "toPrimitive" misspelling
Attempt to explain valueOf/toString coercion between `String(foo)` and `foo + ''`
Move the snippet lower, per https://github.com/ljharb/You-Dont-Know-JS/commit/6331060cab477ab59798a52216847c1e193ac03c#commitcomment-7581066
Merge pull request #181 from ljharb/update_string_coercion

Update string coercion