DOC: install ipython to build RST code blocks properly
DOC: install ipython to build RST code blocks properly

Examples built from Jupyter notebooks use ipython3 in RST code blocks.
This means ipython must be installed for sphinx (particularly
pygments) to pick up the correct lexer. See
https://github.com/spatialaudio/nbsphinx/issues/24

tkphd/pycalphad,tkphd/pycalphad,tkphd/pycalphad