All GSoC projects need proper documentation but in this case we should have a prototypical implementation, for example to access dictionaries at Tools > Options > Language > Writing Aids and I would imagine a wiki page how to do the same on other places.
Please have a look at the suggestions in https://documentation.libreoffice.org/en/join-the-documentation-team/update-help-contents/
Basics done with https://yusufketen.com/post/2020-08-31-libreoffice-gsoc-final-report/. @Olivier: Do you think we need a documentation on the handling? There is no Help button in the dialog, and actually I believe it's self-explanatory.