Add Hyperlane architecture to Intro docs

[anettrolikova]

And improve Introduction

• Introduction should look like:
  • about hyperlane - explain, overview, yep now its time to use the fancy pitch deck words,
  • hyperlane architecture - how it works, how smart contracts operate between each other - deep down into the weeds and as detailed as possible, use lego house as example for contracts
    • some content re architecture can be find in [Hyperlane External Pitchbook](https://www.notion.so/Hyperlane-External-Pitchbook-183e71b164cc47b39c2da0fc8e477930)

[anettrolikova]

https://docs.hyperlane.xyz/docs/introduction/readme updated