add separate requirements file for docs, so we can pin docutils version (see https://github.com/sphinx-doc/sphinx/issues/9727)
add separate requirements file for docs, so we can pin docutils version (see https://github.com/sphinx-doc/sphinx/issues/9727)

JuliaSprenger/python-neo,apdavison/python-neo,INM-6/python-neo,NeuralEnsemble/python-neo,samuelgarcia/python-neo