[STABLE-2112]: add example script (#5)

* [STABLE-2112]: add example script * [STABLE-2112]: Update script and add documentation * [STABLE-2112]: add new line * [STABLE-2112]: Update README * [STABLE-2112]: Moved abis in to doc folder * [STABLE-2112]: rewrite script * [STABLE-2112]: update README * [STABLE-2112]: update README * [STABLE-2112]: update README
circlefin · Jan 11, 2023 · d1c2457 · d1c2457
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+
+# Quickstart: Cross-chain USDC Transfer
+
+## Overview
+
+This example uses [web3.js](https://web3js.readthedocs.io/en/v1.8.1/getting-started.html) to transfer USDC from an address on ETH testnet to another address on AVAX testnet.
+
+### Prerequisite
+The script requires [Node.js](https://nodejs.org/en/download/) installed.
+
+## Usage
+1. Install dependencies by running `npm install`
+2. Create a `.env` file and add below variables to it:
+    ```js
+    ETH_TESTNET_RPC=<ETH_TESTNET_RPC_URL>
+    AVAX_TESTNET_RPC=<AVAX_TESTNET_RPC_URL>
+    ETH_PRIVATE_KEY=<ADD_ORIGINATING_ADDRESS_PRIVATE_KEY>
+    AVAX_PRIVATE_KEY=<ADD_RECEIPIENT_ADDRESS_PRIVATE_KEY>
+    RECIPIENT_ADDRESS=<ADD_RECEIPIENT_ADDRESS_FOR_AVAX>
+    AMOUNT=<ADD_AMOUNT_TO_BE_TRANSFERED>
+    ```
+3. Run the script by running `npm run start`
+
+## Script Details
+The script has 5 steps:
+1. First step approves `ETH_TOKEN_MESSENGER_CONTRACT_ADDRESS` to withdraw USDC from our eth address.
+    ```js
+    const approveTx = await usdcEthContract.methods.approve(ETH_TOKEN_MESSENGER_CONTRACT_ADDRESS, amount).send({gas: approveTxGas})
+    ```
+
+2. Second step executes `depositForBurn` function on `TokenMessengerContract` deployed in [Goerli testnet](https://goerli.etherscan.io/address/0xd0c3da58f55358142b8d3e06c1c30c5c6114efe8)
+    ```js
+    const burnTx = await ethTokenMessengerContract.methods.depositForBurn(amount, AVAX_DESTINATION_DOMAIN, destinationAddressInBytes32, USDC_ETH_CONTRACT_ADDRESS).send();
+    ``` 
+
+3. Third step extracts `messageBytes` emitted by `MessageSent` event from `depositForBurn` transaction logs and hashes the retrieved `messageBytes` using `keccak256` hashing algorithm
+    ```js
+    const transactionReceipt = await web3.eth.getTransactionReceipt(burnTx.transactionHash);
+    const eventTopic = web3.utils.keccak256('MessageSent(bytes)')
+    const log = transactionReceipt.logs.find((l) => l.topics[0] === eventTopic)
+    const messageBytes = web3.eth.abi.decodeParameters(['bytes'], log.data)[0]
+    const messageHash = web3.utils.keccak256(messageBytes);
+    ```
+
+4. Fourth step polls the attestation service to acquire signature using the `messageHash` from previous step.
+    ```js
+    let attestationResponse = {status: 'pending'};
+    while(attestationResponse.status != 'complete') {
+        const response = await fetch(`https://iris-api-sandbox.circle.com/attestations/${messageHash}`);
+        attestationResponse = await response.json()
+        await new Promise(r => setTimeout(r, 2000));
+    }
+    ```
+
+5. Last step calls `receiveMessage` function on `TokenMessengerContract` deployed in [Avalanche Fuji Network](https://testnet.snowtrace.io/address/0xa9fb1b3009dcb79e2fe346c16a604b8fa8ae0a79) to receive USDC at AVAX address.
+
+    *Note: The attestation service is rate-limited, please limit your requests to less than 1 per second.*
+    ```js
+    const receiveTx = await avaxMessageTransmitterContract.receiveMessage(receivingMessageBytes, signature);
+    ```