[tldoc] texlive-*.tex macro change for 2023

[Karl Berry]

Hello translators - regarding the TL manual.

For 2023, I was asked to provide "alt text" for the images in the HTML
output. So I had to change the \tlpng macro, etc., to take another
argument. For example, if you look at texlive-en.tex, you'll see that
the first image (line 644) now looks like:

  \begin{figure}[tb]
  \tlpng{basic-w32}{.6\linewidth}{Basic installer screen (Windows)}
  \caption...
  \end{figure}

That {Basic installer screen (Windows)} argument is new. You'll need to
add (the translation of) it to your source, too. Otherwise you'll get
errors about "Argument of \@caption" or "Argument or \@xdblarg" or some such.

There are similar new "alt text" arguments for the other images.

I haven't yet done any real updates of the manual for the 2023 release,
though there shouldn't be much beyond the usual section of news and
minor tweaks. So I just thought I'd mention this TeXnical change now, so
you can either do it in advance, or at least be aware when the time comes.

Happy translating,
Karl