How to whitelist a web site

I've seen a couple of feedbacks in the store of people who wish it was possible to whitelist a web site, i.e. to disable µBlock on a specific web site.

The feature is already available, it is the big power button: it serves to whitelist the current web site, its state will be remembered next time you visit the web site.

Tip: if you press the Ctrl key as you click the power button, this will whitelist only the current web page, not the whole site (true since version 0.3.2.0)