Document the current design for search in GNOME
There isn't a single place that documents how we expect searching in GNOME to work.
The closest we have is https://wiki.gnome.org/Design/OS/Search which is rather outdated and is specific to gnome-shell. A lot of the details should already be documented in the user manual (see #97).
This would also give us a place to document the benefits and the known issues of the current design.