Explainer explainer should explicitly encourage folks to write explainers in plain text or markdown in their spec repro & discourage folks from writing explainers in tools like Google Docs

[hober]

We've encouraged folks a number of times to do this; perhaps we should capture that encouragement in the explainer explainer itself.

Cases where this has come up:

• Form Participation API design-reviews#305 (comment)
• Constant bitrate audio encoding with MediaRecorder design-reviews#540 (comment)
• Review for CSS property "aspect-ratio" design-reviews#559 (comment)

[hober]

cc @alice

[LeaVerou]

As discussed today, the reasons are:

1. Google Docs is proprietary. Yes, so is GitHub, but git is not, the repo always lives somewhere else as well and can be recovered. If Google Docs goes down, the document goes down too.
2. There are many countries that block Google Docs, but fewer that block GitHub.
3. Everyone in standards has a GitHub account, but many don't want a Google account due to privacy concerns.
4. When people share explainers in Google Docs, they are often inadvertently locked down to be company internal or shared with specific people. A GitHub repo can also be locked down, but that's not something that typically happens with open standards documents.