Make Screenshot application discoverable

https://github.com/helloSystem/hello/issues/50#issuecomment-752902787

> Is there something about KDE screenshots that we could learn for helloSystem?

### [graphics/spectacle](https://www.freshports.org/graphics/spectacle/)

In my experience, **[Spectacle](https://invent.kde.org/graphics/spectacle)** is simply the best in its class. Well thought-out in many ways.

Given its feature set and interaction with other apps: not too many dependencies but still, it's probably not 'slim' enough for a slim ISO.