Documents that setup timeout accepts only positive values

What?

In the upcoming v0.54, the setup timeout option gets the validation and starts to accept only positive (>0s) values.

[x] I have used a meaningful title for the PR.
[x] I have described the changes I've made in the "What?" section above.
[ ] I have performed a self-review of my changes.
[ ] I have run the npm start command locally and verified that the changes look good.
[x] I have made my changes in the docs/sources/next folder of the documentation.