Patch to insert brief introduction to Chapter 3 Document classes and update the AMS document classes section of Additional.lyx to reflect changes in 2.4

[Jürgen Spitzmüller]

Am Donnerstag, dem 29.12.2022 um 20:38 +0000 schrieb John Robert
Hudson:
> Please note that the Fact environment has moved from the (Extended)
> to the 
> basic module and that the Assumption and Question environments are
> new to the 
> (Extended) module and so have no proper descriptions in the original 
> description of the key environments.

Committed.

-- 
Jürgen