Add info about not finishing

[tenhobi]

After trying Patrol for a while and not knowing why my tests do not finish when they couldn't find a widget to tap on, etc., I would appreciate a warning in docs for that! 🙏

Also related to #1602

[bartekpacia]

Thanks for this PR @tenhobi!

Small thing: I'm not sure docs/patrol/finders is the right place for it. That section in the docs talks about Patrol finders, which can be used in both widget test and in integration tests. Not all Patrol users use custom finders, some are only interested in native automation, and then they likely wouldn't see this warning.

I think the better place for it would be the Getting Started guide. What you think?

[tenhobi]

I put it there because it's one of few places where timeouts are mentioned. I can move it to getting started section. :)

[tenhobi]

@bartekpacia I moved it to the section you suggested, is this better? ☺️

[bartekpacia]

Yup, thanks!