add Dockerfile, fixes #36

[KiaraGrouwstra]

this request adds a Dockerfile specifying a basic setup of Jupyter including mariadb_kernel, as suggested in #36. i currently build and run this as:

docker build -t mariadb_kernel . && docker run -p 8888:8888 --rm -v $(pwd):/home/jovyan/work --name mariadb_kernel mariadb_kernel

we may need a few tweaks to the file if we'd rather not have it use root user.

once we could get a working Dockerfile in and an image published to Docker Hub, perhaps we could include such usage instructions based on the published image.

[KiaraGrouwstra]

note that for testing local changes to mariadb_kernel, a container spec would instead have pip build from the local directory, e.g.:

FROM jupyter/scipy-notebook
USER root

RUN apt update
RUN apt install -y mariadb-server
COPY . /tmp/mariadb_kernel
RUN pip install /tmp/mariadb_kernel
RUN python3 -m mariadb_kernel.install