Translate remaining french sections in user guide for transifex usage

[ponceta]

For historical reasons, some user documentation is yet not translated to english what makes it difficult to others to translate it to other languages.

See https://qwat.github.io/docs/master/en/html/user-guide/qwat_struct.html

Sections 3.1->3.6

It would be nice if someone or a group of people would agree to translate it to english.

This has to be done on GitHub directly.

ping @kandre