Add an example

[kwalrath]

https://pub.dev/packages/stagehand#-analysis-tab- deducts 10 points because we don't have a demo in the example/ directory. We could probably extract a bit of typical code from one of our plugins.

[domesticmouse]

I think this is really a bug with Pub.dev's analysis - it makes no sense to have an example for a package that isn't a library.

/cc @mit-mit @jonasfj

[mit-mit]

Well, pub.dev don't know if a package should have an example or not. I'd say that's a missing feature.