[Documentation] Add documentation about `sol!` and `abi_encode`

[tcoratger]

Component

sol-types

Describe the feature you would like

In order to obtain the calldata for a function call like:

sol! {
    #[sol(rpc)]
    contract ERC20Contract {
        function balanceOf(address account) external view returns (uint256);
        function allowance(address owner, address spender) external view returns (uint256);
    }
}

let calldata = ERC20Contract::balanceOfCall { account: evm_address }.abi_encode();

It wasn't clear to me that we can do that this way as all the sol! macro examples that can be found here: https://github.com/alloy-rs/alloy/blob/main/crates/contract/README.md require a Provider.

I had to search for a while before I figured out that I could simply use the strategy with abi_encode to achieve the same goal.

As a result, maybe we should add more documentation in the sol-types README or in the alloy-contract README (so I don't know if it's a cross-repo issue) to inform the user of the possibility of carrying out these use cases (and maybe others) without needing to use the provider flow.

Additional context

No response

[DaniPopes]

We have plenty of documentation on the macro itself through doccomments and in the examples repo (rendered in the book).