Write a design document of architecture

[archerny]

Describe This Problem

We have already done some discussions previously, including the goal of Tatris and the main design of its architecture. Members who participated in the initial discussions may already have a basic idea about what we are going to do. But a design document of architecture is still needed. This document would act as an outline that guides subsequent work and an entrance for new participators or users to understand the project.

Proposal

Write the main design doc and place it under docs dir.

Additional Context

no.