Hello,

this patch adds "Qucs-S", a GUI for different circuit simulation
kernels:
  https://github.com/ra3xdh/qucs_s

Currently the package supports only Ngspice simulation kernel, as it is
recommended by the authors and it is readily available in Guix; but in
the future other kernels can be added, namely Xyce (which is in the Guix
too.)