Add a note explaining that the `wheel` requirement that used to be
historically used in documentation was incorrect.  This also explains
why it can frequently be found in existing projects, and what problems
it causes.  I find myself repeatedly explaining it, so I think having
a single official source would be better.

Incorporates suggestions from Anderson Bravalheri.

Configured indicates that the function code's itself would be configured, not that it is used by an external party. Switch verb to "used" to be clearer as to how the function is being used.