docs(architecture): add architecture diagram

[mandarvaze]

Description of change

As discussed on discord, I've created Architecture document.
The markdown file contains the mermaid diagram code.
Benefit of this (over uploading an image) is that we do not need to keep updating the image.
Instead the mermaid diagram code itself can be updated (suing any editor) and changes will be reflected in the rendered image.

How has this been tested? (if applicable)

I verified that the image is correctly rendered using github's built-in editor (preview tab)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 3.31%. Comparing base (c6e20e5) to head (5fbf01b).
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main     #88   +/-   ##
=====================================
  Coverage   3.31%   3.31%           
=====================================
  Files         19      19           
  Lines       2417    2417           
=====================================
  Hits          80      80           
  Misses      2337    2337           

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[orhun]

Thanks!