Fix child process docs

Fix a number of outright errors in child process documentation, as well as improve the general readability of it by using hyperlinks, documenting defaults, ordering the docs consistently, etc.
This paragraph is a little confusing to me. It seems like it should lead into an example, but then, why would one use the integer fd options by wrapping them in a `net.Socket`, when above, it states that whole (resource-backed) streams may be passed into the API?