Fields “Ring” and “Versions” are unclear

[leafac]

As a package author, I was puzzled by the meaning of the fields “Ring” and “Versions”. I thought “Versions” referred to versions of the package I’m publishing, not version exceptions—referring to Racket’s versions.

With some help, I was able to figure everything out, but it wasn’t intuitive, so I believe we should add links to the relevant documentation:

• Ring: http://docs.racket-lang.org/pkg/Future_Plans.html#%28part._short-term%29
• Versions: http://docs.racket-lang.org/pkg/getting-started.html#%28part._.Version_.Exceptions%29