[BUG]: Documentation missing how to use py::nodelete with shared_holder progressive mode

Required prerequisites

• Make sure you've read the documentation. Your issue may be addressed there.
• Search the issue tracker and Discussions to verify that this hasn't already been reported. +1 or comment there if it has.
• Consider asking first in the Gitter chat room or in a Discussion.

Problem description

If i use py::class<MyClass,std::unique_ptr<MyClass,py::nodelete>> I get a compile time error that I should put PYBIND11_TYPE_CASTER_BASE_HOLDER(MyClass,std::unique_ptr<MyClass>) somewhere, should I also put pybind11::nodelete there as well ? I am not sure, should I even be using unique_ptr at all ? I've not seen how to add py::nodelete to the py::smart_holder as it has no template args

Reproducible example code

py::class<MyClass,std::unique_ptr<MyClass,py::nodelete>>

Start with the linked pybind11 documentation and the reproducible py::class<MyClass, std::unique_ptr<MyClass, py::nodelete>> example. Determine how py::nodelete should be used with shared_holder progressive mode and whether PYBIND11_TYPE_CASTER_BASE_HOLDER is required, then document the supported usage and clarify whether unique_ptr or smart_holder is appropriate.