Add README with project overview and run instructions

[Farhad-Shabani]

As it currently stands, the project looks quite bare from the outside; it's not clear what the goals of the project are or how to get started with it. Even from the inside, the bare state of the project makes onboarding onto it challenging. Getting it running will require going over the code and integration tests themselves, as well as a fair bit of trial-and-error.

Our integration tests are designed to test the entire stack together - including the Cairo contracts, CW light client, and relayer - any changes made to one part of the project must be reflected to the others. This is because of the existing Nix setup. Thus, it’s essential for everyone to learn how to run the whole stack and the CI jobs locally. This entails:

1. Setting up the requisite chain binaries locally, preferably using Nix
2. Declaring and deploying contracts on both chains through the user's local machine
3. Running the relayer, preferably using Nix, to send packets via the relayer's CLI and run the integration tests locally

Add a README that includes:

• An overview of the project, briefly explaining what it does and how different parts come together.
• Instructions on how to run the project, including any prerequisites or setup steps, as outlined above.

[rnbguy]

I second this. I always face difficulty with running the Cairo tests.

[soareschen]

Perhaps this would be a good onboarding for @seanchen1991