Add installation instructions for jupyter and jupyterlab

[joliss]

We're limiting the version range in pip install "jupyterlab>=3.0.0,<4.0.0", as I'm getting the following error message if I simply run pip install jupyterlab to get the latest version:

$ jupyter nbextension install --py --symlink --sys-prefix ipytree
usage: jupyter [-h] [--version] [--config-dir] [--data-dir] [--runtime-dir] [--paths] [--json]
[...]

Jupyter command `jupyter-nbextension` not found.