chore: add migration notes from contractkit

packages/sdk/contractkit/MIGRATION.md

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+# Draft: Migration document from Contractkit
+
+Hello devs 🌱 this is a migration path away from contractkit following the [public deprecation notice](https://forum.celo.org/t/sunsetting-contractkit/5337/1) of contractkit. This aims to give examples to help you move to either [ethers](https://docs.ethers.org/) or [viem](https://viem.sh/).
+
+## Initialization
+
+With ethers:
+
+```diff
+- import Web3 from "web3";
+- import { newKitFromWeb3 } from "@celo/contractkit";
+
+- const web3 = new Web3("https://alfajores-forno.celo-testnet.org");
+- const kit = newKitFromWeb3(web3);
++ import { providers } from 'ethers'
++
++ const provider = new providers.JsonRpcProvider('https://alfajores-forno.celo-testnet.org')
+```
+
+With viem:
+
+```diff
+- import Web3 from "web3";
+- import { newKitFromWeb3 } from "@celo/contractkit";
+-
+- const web3 = new Web3("https://alfajores-forno.celo-testnet.org");
+- const kit = newKitFromWeb3(web3);
++ import { createPublicClient, http } from 'viem'
++ import { celo, celoAlfajores } from 'viem/chains'
++
++ const client = createPublicClient({
++   chain: celoAlfajores, // or celo for celo's mainnet
++   transport: http()
++ })
+```
+
+## Basic usage
+
+While we cannot here show all the use-cases of contrackit or ethers or viem, let's try to give an overview of how they can be used for different goals.
+
+### Get address
+
+With ethers:
+
+```diff
+- const accounts = await kit.web3.eth.getAccounts();
++ const accounts = await provider.listAccounts();
+const defaultAccount = accounts[0];
+```
+
+With viem:
+
+```diff
+- const accounts = await kit.web3.eth.getAccounts();
++ const accounts = await client.getAddresses()
+const defaultAccount = accounts[0];
+```
+
+### Get wallet
+
+With ethers:
+
+```diff
++ import { Wallet } from 'ethers'
+
+- const wallet = kit.getWallet();
++ const wallet = new Wallet('0x...', provider);
+```
+
+With viem:
+
+> [viem does not currently support](<[source](https://viem.sh/docs/ethers-migration.html#viem-11)>) client-side signing (it's coming shortly!) – until then, you can use an Ethers Wallet
+
+### Provider methods
+
+With ethers:
+
+```diff
+- const provider = kit.connection.web3.currentProvider
+- kit.connection.getBlock(...)
+- kit.connection.getTransaction(...)
+provider.getBlock(...)
+provider.getTransaction(...)
+```
+
+With viem:
+
+```diff
+- const provider = kit.connection.web3.currentProvider
+- kit.connection.getBlock(...)
+- kit.connection.getTransaction(...)
++ client.getBlock(...)
++ client.getTransaction(...)
+```
+
+### Signer methods
+
+With ethers:
+
+```diff
+- const provider = kit.connection.web3.currentProvider
+- const signer = provider.getSigner(kit.connection.defaultAccount)
++ const signer = provider.getSigner(address)
++ signer.sendTransaction(...)
++ signer.signMessage(...)
+```
+
+With viem:
+
+```diff
+- const provider = kit.connection.web3.currentProvider
+- const signer = provider.getSigner(kit.connection.defaultAccount)
++ const [address] = await client.getAddresses()
++ const account = getAccount(address)
++ client.sendTransaction({ account, ... })
+```
+
+### Contract interaction
+
+I'll show the most "basic" interaction, which is a CELO transfer:
+
+With ethers:
+
+```diff
++ import { tokenAbi } from './abi.json'
+- const CELO = await kit.contracts.getGoldToken();
+- const txReceipt = await CELO.transfer('0x...', amount)
++ const tokenAddress = '0x...'
++ const contract = new ethers.Contract(tokenAddress, tokenAbi, signer);
++ const txReceipt = await contract.transfer('0x...', amount);
+```
+
+With viem:
+
+```diff
++ import { tokenAbi } from './abi.json'
+- const CELO = await kit.contracts.getGoldToken();
+- const txReceipt = await CELO.transfer('0x...', amount)
++ const tokenAddress = '0x...'
++ const transfer = await client.simulateContract({abi, address: tokenAddress, functionName: 'transfer' })
++ const txReceipt = await transfer('0x...', amount);
+```
+
+For more in depth examples, I highly recommend checking out the extensive documentations of both [ethers](https://docs.ethers.org/) and [viem](https://viem.sh/).