Add three `systemd` user units that reset
volume, screen brightness, and keyboard backlight,
so that every session starts from a known state.
Values come from ~/.config/environment.d/50-defaults.conf,
and can be overridden per machine via an untracked 90-local.conf
- Follow XDG standard: ~/.config and ~/.local folders
- Set environment variables and define aliases within ~/.config/shell
- Add installation script for easy setup and maintenance
(i.e., `dotfiles-install` and `dotfiles-update`)
- Add README.md with info on the installation and general notes
