first draft of TPAC talk

The first draft is here:
https://w3c.github.io/mathml-docs/TPAC-2021/index.html

It acts like a normal slide show, so click on the title slide and then use
arrows or space bar to walk through it.

If you have comments or see problems, open an issue
<https://github.com/w3c/mathml-docs/issues>, or if that is problematic,
send me email.

The talk is on Monday (early morning for me), so all comments need to be on
Sunday or they won't get acted upon.

    Neil