non-NixOS:
bundle install
bundle exec jekyll serve --livereload
NixOS:
nix-shell
regenerate gemset.nix, following Run Jekyll locally on NixOS by Wout Swinkels:
nix-shell -p bundler bundix
bundle config set path vendor
bundle config set --local force_ruby_platform true
bundle cache --no-install
bundix
rm -rf vendor
rm -rf ~/.cache/bundix
exit