bug#19793: please document level of R7RS[-small] support in Guile manual

[address@hidden]

It would be nice if the Guile manual described to what extent Guile supports R7RS[-small],

and what R7RS features are still missing.

Something along the lines of https://lists.gnu.org/archive/html/guile-devel/2012-02/msg00065.html

but up to date.

thanks