DOC: Handle missing nbconvert in html build
Closes https://github.com/pandas-dev/pandas/issues/16329
fine, though to be honest I would just fail and have users install ``nbconvert`` its not a big deal. (IIRC its already in the doc-install requirements anyhow). Both approaches would be OK for me Agreed that installing nbconvert isn't a big deal, but since I've already written it this way I'll be lazy and just keep it :)