fix: change license of contracts

[dristpunk]

Closes BES-95

[linear]

BES-95 Change license to MIT

1. In Greeter.sol, change

// SPDX-License-Identifier: UNLICENSED

To

// SPDX-License-Identifier: MIT

2. Add LICENSE file, like this one: https://github.com/defi-wonderland/foundry-mock-generator/blob/c9d4cfc967fce7f64034d339a5d8d555096f3607/LICENSE
3. Mention the license in package.json: "license": "MIT"
4. Mention the license in the README

Licensing
The primary license for the mock generator is MIT, see LICENSE.

[0xGorilla]

Is it OK for the out directory to exist in git?

[0xRaccoon]

mm I agree this should be generated when building and should be removed

[dristpunk]

.gitignore says that

# Keep related abi
out/*/*
!out/Greeter.sol/*

don't we really need it in boilerplate?

[0xJabberwock]

I agree that Greeter output is not worth keeping.

[0xRaccoon]

The out folder should be removed. Other than that, it looks good to me