First document upon opening YNAW#248

We would like to have a configurable first document upon opening YNAW. It could maybe configurable to be different for each user (reader/editor), since most of the users will be starting deeper in the interlinked document tree (in their relevant field).

Maybe also a Home button visible on each page to go to this document.

My thinking was somewhat similar, I want to be able to add to the homepage of the wiki, so it doesn’t just have the file structure. Somethinking an intro message would be really great to add.

https://github.com/pingcap/gdocwiki supports displaying README files at any point of the hierarchy