consider history section in readme

[pkra]

It might be worthwhile to keep a bit of that history in the readme.

From #537 (comment)

loosely, it started under the W3C's HTML working group where Steve Faulkner created it. Then it became the web apps working group. Now it's under the ARIA working group. Dates could be found by spelunking the commit log.

[pkra]

I can't set a label but this would be "editorial".