Added high-level diagrams representing the typeshed codebase.

You can see how they render in GitHub here: https://github.com/CodeBoarding/GeneratedOnBoardings/blob/main/typeshed/on_boarding.md

The idea of these diagrams is to help new contributors get up-to-speed with the existing codebase. We think here visuals are crucial as they give you enough context to concentrate on the interesting to you component. We also believe that such documents require a lot of effort from the maintainers so we are looking into creating github action which generates them, the generation is using both static analysis and LLMs.

Any feedback is more than welcome! I usually open discussions, but it seems like they are not enabled for this repo so I decide to open directly a PR.

Full disclosure: we're trying to turn this into a startup, but we're still in a very early stage and figuring out what will actually be useful for people.