DOC: Add Matti Picus to steering council in new website
DOC: Add Matti Picus to steering council in new website

Per announcement in https://mail.python.org/pipermail/numpy-discussion/2020-June/080760.html.

Partial overlap with dev/governance/people.html in the numpy/numpy repo
(see PR #16757).

numpy/numpy.org,numpy/numpy.org,numpy/numpy.org,numpy/numpy.org