Apparently, I succeeded in doing it, because I found an html copy of my site in a directory called localhost. (I'm running Ubuntu under Windows 10).
Parsoid seems properly installed. The command "curl -L http://localhost:8142/localhost/v3/page/html/Main_Page/ " gives the expected result and my website "http://localhost/mediawiki/" uses "VisualEditor".
My first question : how do I instruct Parsoid to start converting my whole site?
And secondly: how can I learn Parsoid to add ".html" to the links it creates ? At present it makes links like "<a href="/mediawiki/index.php/Dossier:Drebbels_Thermometer" title="Dossier:Drebbels Thermometer">"
Thanks in advance