* fix: update linux build dependencies for libpng
- add libpng to linux build docs
- add libpng to nix build file
* linux docs: reformat code blocks
- add code block bash syntax highlighting
- format long code blocks to multiline
* Add nix-shell to allow native build on NixOS
* Remove unnecessary README for nix. Move major comment to shell.nix
* Update path in building-linux.md
* Use cached nix packages from unstable channel
* Add proper license to nix shell