Add a short prompt on how to get the app id-s

[alshopov]

Is your feature suggestion related to a problem? Please describe.
Had some trouble finding what to put in the lists of apps in Preferences...->Blacklists

Describe the solution you'd like
A small help or popup label or direct explanation you can get the identifier of a bundle by executing:
mdls -name kMDItemCFBundleIdentifier /Application/Bothersome.app

Describe alternatives you've considered
Otherwise you have to search the answer on stack overflow or Apple dev docs.

[lwouis]

Closing this ticket in favor of #539. There are better way to improve the UX than explain how to run a terminal command to get a bundleID. It's still a good option as it's easy to add, but we may want to get the extra mile and put an app picker UI for instance.