Draft: DOC minor update to doc

I modified a bit the doc. A preview is available at https://docs.iota2.net/ I still get a lot of warnings when building the doc, some of them resulting in lower output quality but I will address those in an other MR.

(I'm not familiar yet with git flow commands, hence the strange name of the branch) (I do not have write access to the main repo yet, that's why I request a merge from my fork)