My thought was to add something like this to the top of functions.rst:

```
Note that some of the functions listed here have the :ref:`default return value <tut-defining-functions> of ``None``.
```

For reference, the builtins this applies to are:

* breakpoint()
* delattr()
* exec()
* help()
* print()
* setattr()

Which makes me wonder if the hint is even worth having, since it's so few of them.

Note that of these, exec() does what this ticket originally proposed for print() - i.e. it explicitly says that the function returns None.