docs: Add an ARCHITECTURE.md file

[kurosakishigure]

Page Link

https://github.com/kurosakishigure/katharsis

What is the documentation issue?

We are missing an ARCHITECTURE.md file to describe the overall architecture of the project.

Is there any context that might help us understand?

Including an ARCHITECTURE.md file will make it easier for contributors to understand the project.

[github-actions]

The issue was marked with the good first issue label by a maintainer.

This means that it is a good candidate for someone interested in contributing to the project, but does not know where to start.

Note

To get started, read the Contributing Guide.