gp: add venv + ipykernel notes

BLcourse2.3/README.md

@@ -8,4 +8,19 @@ $ jupyter-notebook notebook.ipynb
 ```
 
 For convenience the ipynb file is included. Please keep it in sync with the py
-file using jupytext.
+file using `jupytext` (see `convert-to-ipynb.sh`).
+
+One-time setup of venv and ipy kernel:
+
+```sh
+# or
+#   $ python -m venv --system-site-packages bayes-ml-course-sys
+#   $ source ./bayes-ml-course-sys/bin/activate
+$ mkvirtualenv --system-site-packages bayes-ml-course-sys
+$ pip install -r requirements.txt
+
+# Install custom kernel, select that in Jupyter. --sys-prefix installs into the
+# current venv, while --user would install into ~/.local/share/jupyter/kernels/
+$ python -m ipykernel install --name bayes-ml-course --sys-prefix
+Installed kernelspec bayes-ml-course in /home/elcorto/.virtualenvs/bayes-ml-course-sys/share/jupyter/kernels/bayes-ml-course
+```