Hi Jim,
Thanks for offering to help 
Like Processing.py itself, the website isn’t actively maintained, but I did upgrade it a while ago so it now builds and deploys automatically to Netlify, which makes changes easier. You can open a Pull Request to this repository to add a reference to py5.
The right balance, I think, is to note that Processing.py still works with Processing 3.5.4, but to encourage people to use py5 with Thonny if they need Python 3 or deeper integration with the Python ecosystem. This post is a good reference: Py5 vs Processing.py - #2 by tabreturn
Once there’s a working PDE mode for py5, we can revisit the website and make the deprecation of Processing.py more explicit.
Let me know what you think.
Cheers,
Raphaël