"Teach your employees that if you don’t want to be interrupted you better write good documentation."

And reward them for doing it.

If your company do "360 degree" evaluations where your peers praise you for your quick answers to their questions, you are effectively incentivised to NOT document and instead be interrupted...

It's not something to be taught. For majority of devs an average working day is too short to do everything they theoretically should. So they make choices based on feedback/motivation which rarely favors writing good docs over writing more code. On top of that many good devs are simply unable to write comprehensible documentation because its very different kind of skills, or just because English is not their native.

I would be inclined to say that interruptions to help your colleagues should be accepted. Writing good documentation is actually hard and if you not willing to invest the time to do it well and to make sure the documentation can be found when needed you had better not write documentation at all.