Suggest adding guideline about JupyterHub to the docs

[LawrentChen]

Hi, Kyle and other developers. First I want to thank you for your wonderful stata_kernel! 👍

I would suggest adding guideline about JupyterHub to the docs, maybe in the Getting Started and Configuration chapters I guess, and I think nothing has to change in the code.

As I followed the docs to install stata_kernel, it mostly went well, but I didn't notice the difference of deployment between Lab and Hub at first. Then it took me quite a few hours to figure out the problem and finally got to #222 and #327 😭. Now that you have already add the global configuration feature in release 1.11.0, it should be good to let new users know how to use it correctly.

Here are my personal experience on installation (though I think you may have already well known, just for your reference😂):

1. I have deployed a JupyterHub using The Littest Jupyter Hub(TLJH) on Ubuntu 18.04.4, and the following steps are supposed to be run by the root account of server.
2. Install Stata.
3. Install the stata_kernel in the Hub's user environment by adding path temporarily export PATH=/opt/tljh/user/bin:${PATH}, then pip install stata_kernel and python -m stata_kernel.install. This environment is avaliable to all users of the Hub, see accessing-user-environment-outside-jupyterhub).
4. Since my stata license is a short-term usage on the SE version, I need to change the stata_path(default is MP version) in configuration file ~/.stata_kernel.conf, and also mannually copy and rename this file to /etc/stata_kernel.conf in order to let it be the global configuration. Then new users will automatically copy this file to their own home directory when they first invoke stata notebook in the Hub, and they can still override global config by editing their own ~/.stata_kernel.conf. Here it might be a good idea to put a default conf file as an example in the Configuration chapters. Because if someone change the content by mistake(like what I did😭), it seems they will have to rm that file and pip uninstall then install stata_kernel to get back the original one...
5. jupyter kernel list to list the existing kernel, jupyter kernel uninstall stata to remove the stata_kernel(different from pip uninstall stata_kernel)

Again, my gratitude to your awsome work. Appreciate that!