feat: update README.md (#57)

README.md

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 The Smart Account is the contract implementing the ERC-4337 standard. Its address is deterministically computed from the public key of the user. This contract implements all the logic to verify signatures, effectively allowing the user to operate onchain actions thanks to their passkey. The contract is not deployed when the passkey is generated to avoid paying huge gas fees for a contract that might never be used. Instead, it is deployed when the user first interacts with the contract.
 
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 ## Onchain interactions via UserOperations
 
 The ERC-4337 standard revolves around UserOperations, which are basically objects replacing transactions and that are sent on behalf of the user by nodes known as [`Bundlers`](https://docs.stackup.sh/docs/erc-4337-bundler#:~:text=In%20ERC%2D4337%2C%20a%20Bundler,work%20on%20any%20EVM%20network.). UserOperations are signed by the user with their passkey and the bundler's job is to include them in a block while taking a little fee for the work. In our case, we use the [StackUp Bundler node implementation](https://docs.stackup.sh/). We strongly advise you to look at Stackup documentation and the ERC-4337 EIP to understand how Bundlers work.