Plugin to download metadata from BiblioNETka <https://biblionetka.pl>.
Calibre documentation here <https://manual.calibre-ebook.com/creating_plugins.html>, here <https://manual.calibre-ebook.com/develop.html> and here <https://manual.calibre-ebook.com/plugins.html> contains useful hints.
To load plugin in calibre run calibre-customize -b . In case callibre is installed system-wide, it's advised to run your favourite tool with with adjusted PYTHONPATH pointing to calibre imports, e.g PYTHONPATH=$PYTHONPATH:/usr/lib/calibre/ vim.