Add a folder to git with exceptions

Given this folder structure:

app
├── bin
│  └── parse-ansi-codes.rs
├── Cargo.lock
├── Cargo.toml
├── README.md
├── src
│  ├── cursor.rs
│  ├── lib.rs
│  └── style.rs
├── target
│  └── debug
└── test

I can add the entire app directory to git, while ignoring the bin folder:

$ git add . ':!bin'

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