Reorganized a bit and added comments about what will eventually disappear.

Author: nthiery

Dockerfile

@@ -2,20 +2,21 @@ FROM sagemath/sagemath:8.0
 
 # Inspired from https://mybinder.readthedocs.io/en/latest/dockerfile.html#preparing-your-dockerfile
 
-ENV NB_USER sage
-ENV HOME /home/${NB_USER}
+ENV NB_USER=sage
+ENV HOME /home/sage
 
-# Make sure the contents of our repo are in ${HOME}
-COPY . ${HOME}
-USER root
-COPY jupyter jupyter-notebook /usr/bin/
-RUN chown -R ${NB_USER}:${NB_USER} ${HOME}
-USER ${NB_USER}
-
-# Upgrade to jupyter 5.* as required by mybinder
+# Upgrade to jupyter 5.* as required by mybinder and install additional kernels
+# This will eventually be lifted upstream to sagemath/sagemath
 RUN sage -pip install "notebook>=5" "ipykernel>=4.6"
-
-# Install additional kernels
 RUN sage -i gap_jupyter
 RUN sage -i singular_jupyter
 RUN sage -i pari_jupyter
+
+USER root
+# This will eventually be lifted upstream to sagemath/sagemath
+COPY jupyter jupyter-notebook /usr/bin/
+
+# Make sure the contents of our repo are in ${HOME}
+COPY . ${HOME}
+RUN chown -R ${NB_USER}:${NB_USER} ${HOME}
+USER ${NB_USER}