docs: loading contract from sol file fixed

[Aviksaikat]

Summary

This is not the proper way to load solidity files per alloy=0.5.4.

sol!(
    Counter,
    "artifacts/Counter.sol"
);

Problem

names are not allowed outside of JSON ABI

It should be

sol!(
    "artifacts/Counter.sol"
);

Example

The following snippet worked perfectly

sol!(
    // IUniswapV2Factory,
    "contracts/IUniswapV2Factory.sol"
);

[zerosnacks]

Thanks @Aviksaikat!

Related: alloy-rs/core#636 (comment) / https://github.com/alloy-rs/core/pull/647/files