Auto merge of #1365 - ches:docs, r=brson

While reading through the docs, this section broke my concentration even though the functionality's purpose is fairly obvious, because of a grammatical agreement problem and some redundant/wordy terms. I hope this is an improvement.

A couple of other minor changes:

1. "Limitations" sound like things Cargo is *incapable* of doing. The points here are conscious decisions, so calling them "restrictions" seemed more appropriate to me.
2. TOML's source is linked to on the FAQ page, but I'm pretty likely to land directly on the Configuration page from a search, so a direct link from there seemed helpful.

r? @steveklabnik for docs.