How is it more convenient to wikidate new entities in a project and maintain documentation?

Question

Backend

with the arrival of the second person in the backend department, it became difficult - there was no time to delve into who was doing what due to the heavy workload, and then I had to immediately understand the entities created by my partner. Now my partner is gone and I'm preparing for the arrival of a new one. Together with the management, we decided that we would add each entity to a certain reference book where there would be a brief description of this entity and key points. This will allow any new programmer to read and understand what's what. Only it would be desirable that still visually it was possible to show communications between entities.

Advise what tools are suitable for this.