Hello!
Ah, sorry! Wiki files are not displayed in Godot3 editor due to "wiki" extension. Or at least I don't know how to make them visible. In order to edit them, it is necessary to use an external text editor, see example image attached.
In Godot4 editor it is possible to add "wiki" extension in "editor settings/Docks/FileSystem/TextFile Extensions". But it is only for "dev" branch for now. Sorry for inconvenience!
