[racket] Standard references in the docs

Matthias Felleisen wrote:

> As for the language itself, we cannot distinguish which feature comes from where and,
> honestly, I think it would be asking a bit much.  I am old enough, but I honestly don't
> recall when with-input-from-file was added to some R^nRS: n = 3, 4, 5, or 6? Finally,
> since Racket isn't Scheme or CL or Clojure, we are also reluctant to annotate for/fold
> with "warning this is not a feature you will find in some implementation of CL or
> Clojure or Scheme." I hope you understand

I see these problems, but I disagree a bit. It can be really useful to look
beyond the Racket implementation of a certain feature subset by reading
the original spec, and you can judge the portability of your Racket program
to other languages in the Scheme tradition better.

As for finding specs, I think at least in the case of SRFIs it is easy.

In case I get to this, would patches be appreciated?

Thanks again.

  Leslie