Default `--flake` to `~/.config/system-manager`

[ntninja]

Is your feature request related to a problem? Please describe.

I only quickly tried out system-manager (looks pretty cool), but having to add --flake ~/.config/system-manager to every command seems rather redundant given that ~/.config/system-manager is the obvious implied default set by system-manager init.

Describe the solution you'd like

Make --flake optional and let it default to `~/.config/system-manag´.

Describe alternatives you've considered

None, my ideas are always perfect. 😉