boost::python::vector_indexing_suite doc strings

[CEXT-Dan]

Hi,

in my project, I generate .pyi files from doc strings, but I'm unsure how to add my doc strings to boost::python::vector_indexing_suite, specifically to append and extend as base_append and base_extend are private, help a newb : )

https://github.com/CEXT-Dan/PyRx/blob/d9fe3006695ae2866754d0177cafd3fc59f328e0/PyRxCore/PyDbObjectId.h#L47
https://github.com/CEXT-Dan/PyRx/blob/d9fe3006695ae2866754d0177cafd3fc59f328e0/PyRxCore/PyDbObjectId.cpp#L13-L14