When we need to add developer notes w.r.t designs or implementation or even left out pieces of any aspects, it gives us better manageability to use notebooks directly than attaching files from drives/machines.
If Aha has a wiki, this request doesn't make any sense. We are thinking of using notebooks feature as a replacement/alternative to having a wiki embedded
There is a wiki available in the Product -> Notes tab. You can add content here and export it directly to a Notebook.