docs: add architecture overview of apphash.io

[qj0r9j0vc2]

I think if there is any overview of this architecture how apphash.io works, it must be useful for users who are considering to adopt it to their system.

[zsystm]

@qj0r9j0vc2
Thanks for the feedback. 👍 I love this personally.
Let me add this diagram.