ground flat-file dependencies in guix / nix #70

To make flat-files of my "qtrx" GnuCash DB suitable for version control, I use a Makefile that depends on a few things not in the directory:

• sqlite3
  • I use the one from Ubuntu / debian.
• sqlite-diffable by simonw
  • installed with pipx; noted version: 9a6d64d Aug 18 2022
• finquick
  • I point to my working copy with use FINQUICK=~/projects/finquick/packages/brcal.