Improved docstring of AttrTree.__dir__
Improved docstring of AttrTree.__dir__

vascotenner/holoviews,basnijholt/holoviews,basnijholt/holoviews,ioam/holoviews,vascotenner/holoviews,vascotenner/holoviews,ioam/holoviews,basnijholt/holoviews,ioam/holoviews