NixOS Branding Guide v0.1.0

"### Added

• Initial release
• Typst file for creating the document.
• package.nix for build
• editable.nix for development
• common.nix for shared nix derivation attributes
• README.md has general information about the guide and contributing
• data/ contains the version file
• images/ contains the cake SVG file
• This CHANGELOG.md file
  "