Feature suggestion: alt-screen with flag/ keymap

[nkxxll]

As I worked on the app I had the idea to add a flag for an alt-screen option which centers the timer in the middle of an alt-screen in the terminal at start up. You could even add a keybinding to toggle from alt-screen to normal view.

@caarlos0 if you like the idea I would love to make a PR in the next time.

[caarlos0]

I think a flag to start it in altscreen would be cool, yeah

[nkxxll]

On it ;) 👍