[css-typed-om-1] Typed OM changes section

[svgeesus]

The ED of Typed OM is dated 15 June 2021 while the /TR version is 10 April 2018.

So it is due for republishing, but there is no changes section. There have been many changes

[svgeesus]

@tabatkins this could really do with a republish. Can you tackle a changes section?

[svgeesus]

Let's get a new WD published before we hit the 8-year anniversary of any update, next month.

I will put together a changes section.