add practice projects

practices/hello-package/Readme.md

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+## Hello Package
+A practice project used in [Crate and Module](https://practice.rs/crate-module/crate.html) chapter.
+
+This project will guide us to create a package with a binary crate and several library crates in it.
+
+The project structure is as below:
+```shell
+.
+├── Cargo.lock
+├── Cargo.toml
+├── Readme.md
+├── src
+│   ├── back_of_house.rs
+│   ├── front_of_house
+│   │   ├── hosting.rs
+│   │   ├── mod.rs
+│   │   └── serving.rs
+│   ├── lib.rs
+│   └── main.rs
+```