[FEATURE] Add link to created files to central index

[timmb]

Thank you for creating this excellent plugin!

Is your feature request related to a problem? Please describe.
I want to have all my highlights linked to from a single file that I can browse and keep organised.

Describe the solution you'd like
When a new file is created (because a highlight is in a new book), I'd like a link to this new file to be added to the bottom of a file I specify.

Describe alternatives you've considered

I could add the links manually, but I have to keep sweeping for orphaned links and it's cumbersome to keep up to date.

I could give up on having a central index, but it's useful for me to be able to browse through my links, and to group these links by topic, etc.

Additional context