Combine documentation in `doc` and `src/doc`

There is no reason to have two locations with overlapping content. It is confusing and people do not know where to find the necessary information.

added BugConfirmed label

assigned to @timm

changed iteration to Sprint Apr 3, 2023 - Apr 16, 2023

added Statusnext label

removed iteration Sprint Apr 3, 2023 - Apr 16, 2023

changed iteration to Sprint Apr 17, 2023 - Apr 30, 2023

added Statustodo label and removed Statusnext label

set weight to 12

added (- (E labels

added P2 label

changed milestone to %LinkAhead Relaunch

assigned to @daniel and unassigned @timm

added Statusdoing label and removed Statustodo label

Old documentation was moved already in 6b2fc62b, at least for most parts. I am doing a verification now.

mentioned in merge request !93 (merged)

added StatusReview label and removed Statusdoing label

assigned to @timm and unassigned @daniel

closed

removed StatusReview label

assigned to @daniel and unassigned @timm