feat: Add Binder support (#23)

* Add minimal Dockerfile for repo2docker to build and launch successfully
  from matthewfeickert/pythia-python:pythia8.308.
   - Constrain 'jupyter-server<2.0.0' to avoid
     jupyterhub/repo2docker#1231 and
     jupyter-server/jupyter_server#1038
* Add binder_repo2docker Make target for local building with repo2docker.
* Add Binder launch badge to README.

Author: matthewfeickert

Diff for: Makefile

@@ -48,3 +48,8 @@ test_fastjet:
 		--volume $(shell pwd):/work \
 		matthewfeickert/pythia-python:latest \
         'g++ tests/test_FastJet.cc -o tests/test_FastJet $$(fastjet-config --cxxflags --libs --plugins); ./tests/test_FastJet'
+
+binder_repo2docker:
+	repo2docker \
+	--image-name matthewfeickert/pythia-python:binder \
+	.

Diff for: README.md

@@ -2,6 +2,7 @@
 
 [![Docker Pulls](https://img.shields.io/docker/pulls/matthewfeickert/pythia-python)](https://hub.docker.com/r/matthewfeickert/pythia-python)
 [![Docker Image Size (tag)](https://img.shields.io/docker/image-size/matthewfeickert/pythia-python/latest)](https://hub.docker.com/r/matthewfeickert/pythia-python/tags?name=latest)
+[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/matthewfeickert/pythia-python/HEAD)
 
 > PYTHIA is a program for the generation of high-energy physics events, i.e. for the description of collisions at high energies between elementary particles such as e+, e-, p and pbar in various combinations.
 

Diff for: binder/Dockerfile

@@ -0,0 +1,40 @@
+FROM matthewfeickert/pythia-python:pythia8.308
+
+# Remove existing non-root user "docker" with uid 1000
+# to avoid conflict with jovyan
+USER root
+RUN deluser docker
+
+ARG NB_USER=jovyan
+ARG NB_UID=1000
+ENV USER ${NB_USER}
+ENV NB_UID ${NB_UID}
+ENV HOME /home/${NB_USER}
+
+USER root
+RUN adduser --disabled-password \
+    --gecos "Default user" \
+    --uid ${NB_UID} \
+    ${NB_USER}
+USER ${NB_USER}
+
+# FIXME: Downgrade jupyter-server to contend with:
+# https://github.com/jupyterhub/repo2docker/issues/1231
+# https://github.com/jupyter-server/jupyter_server/issues/1038
+RUN python -m pip --no-cache-dir install --upgrade \
+    notebook \
+    jupyterlab \
+    jupyterhub \
+    'jupyter-server<2.0.0'
+
+# Make sure the contents of the repo are in ${HOME}
+COPY . ${HOME}
+USER root
+RUN chown -R ${NB_UID} ${HOME} && \
+    chown -R ${NB_UID} /usr/local/venv
+USER ${NB_USER}
+WORKDIR ${HOME}
+
+# Null out ENTRYPOINT and CMD to let repo2docker control them
+ENTRYPOINT [ ]
+CMD [ ]