Document solidity contracts

[gjermundgaraba]

Move any top level documentation about the solidity contracts to contracts/README.md and link to them from the root readme file.

It should be easy for someone who doesn't know the setup to go in and get a good overview over how the system works and how the different contracts interact.

Make sure the new README has at least the following:

• Purpose and intended use case
• High level architectural diagram with Mermaid
  • The main contracts should be outlined and made clear how they work together
• How to build and test
• How to integrate/use

[HMSagar2701]

Hi @gjermundgaraba , Can I work on this issue ?

[gjermundgaraba]

Hi @HMSagar2701, thanks for the interest, but I was thinking maybe the team should take this one on as it requires quite deep understanding of all the components. If you anyway feel like you would be able to deep dive into how it works and do this, I will not stop you from making a PR which I will happily review :)