Update lyx-2.4 docs

[Pavel Sanda]

On Sun, Jan 29, 2023 at 05:37:30PM +0100, Jürgen Spitzmüller wrote:
> Am Sonntag, dem 29.01.2023 um 17:23 +0100 schrieb Jean-Pierre Chrétien:
> > I would like to search easily what has been updated since (but for
> > the new index 
> > features that I have  already updated in the UserGuide).
> > Is it possible to search for modifications after a given date in the
> > documents ?
> > I could search for changes in Trac, but is is quite lengthy.
> 
> Document > Track Changes > Accept and Reject Changes. This dialog has
> the change dates (not ideal for sure).

Not ideal either but, if you can track down commit hash which you 
already covered and count of the commits to manual since then (you could use something like:
git log  {SHA_of_20_month_old_commit_not_translated_yet..HEAD path_to/manual.lyx | grep ^commit|wc -l
)

Then take that count number and use File->Version control->Compare with older Revision
and fill up that number into Revisions back.

Pavel