Guile-JSON now seems to be a required dependency

[Timothy Sample]

Hello all,

I just tried to build Guix from source and got an error:

    ERROR: no code for module (json)

It looks like the new “swh.scm” module (which is really cool!) makes
Guile-JSON a required dependency.  I’m not sure if this is intentional.
If it is, the “Requirements” section of the manual needs an update.

I was able to build Guix using the same build script without Guile-JSON
on commit 5e369f8ab9e230193194b4d5846a5c78bbc89943.


-- Tim