Work before Web Engines Hackfest

[spectranaut]

Work to do before WEH and Igalia week:

• demo of running WPT prototype on linux (working)
• demo of running WPT protoype on mac (working)
• slides explainer for WEH breakout discussion (in progress)
• instructions for running on mac -- what do we need to install for ModuleNotFoundError: No module named 'ApplicationServices'
• how to present the code in the presentation, should we just link to this PR? I've been keeping the issue description up to date, we should add some notes about running on mac: Experiments with extending testdriver.js for platform accessibility API testing wpt#2