How do I add python3 kernel to jupyter (IPython)

This worked for me on Ubuntu 16.04:

python2 -m pip install ipykernel
python2 -m ipykernel install --user

python3 -m pip install ipykernel
python3 -m ipykernel install --user

Reference to the documentation:
Kernels for Python 2 and 3. Installing the IPython kernel – IPython Docs.