[latexrefman] Suggestion for future update

[Pablo González L]

Hi, first of all I'm just giving birth thanks for the great work :-)
A note for the future, with the changes introduced in 2020 (`-dev`) and that
will be implemented directly at some point, you will be able to use `xparse`
for new commands and environments, will you be able to add a comment of this in
the future version?

Apart (I don't know if it goes in this list, but they are the same authors and
it is related)

The file `latex-doc-ptr` may need to be updated a little bit, some links are
broken and the reference name to this guide is a bit strange (LaTeX: Structured
documents for TEX) and it is an important file since it is the one that throws
`texdoc latex` by default and it is the first thing that new users look for.
Greetings
Pablo