Working towards 0.1 MVP release

[kenliu]

Features to implement for the v0.1 release:

Features

• handle default packages
• install default packages using dnf
• install packages using flatpak
• install script packages
• clean up built in help output
• implement homebrew support
• homebrew cask support
• implement dry-run mode #2

Documentation and project stuff

• finish updating sample metapkg.kdl annotated file
• create simple example file
• add quickstart doc to readme
• add basic usage info to readme
• update docs on supported package managers

Infra and testing

• set up release tooling