relies on pandoc + live-server

I wanted a live markdown viewer and made this list. They mostly rely on node and hence can be tough to configure (tried packaging markdown-preview.nvim but had some issue). I managed to package vim-livedown too but one markdown viewer is enough.

davidgranstrom/nvim-markdown-preview
euclio/vim-markdown-composer
iamcco/markdown-preview.nvim
JamshedVesuna/vim-markdown-preview
shime/vim-livedown

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.