New Guix reference card

[Ludovic Courtès]

Hello Guix!

I’ve written a reference card for Guix, which you can find here:

  https://gnu.org/s/guix/guix-refcard.pdf

The source is at:

  https://git.savannah.gnu.org/cgit/guix/maintenance.git/tree/doc/refcard

It’s written using the Lout document formatting system, so I provided a
simple build file such that you just have to run:

  guix build -f build.scm

I initially tried to do this in plain TeX based on the Org-mode and GDB
refcards, on the grounds that people were more likely to be familiar
with TeX, but that turned out to be too tricky for me and I’m just more
fluent in Lout than in TeX.

Enjoy, share, and improve!  :-)

Ludo’.