init: add rust console app and submodule

.gitmodules

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+[submodule ".externals/awesome-design-md"]
+	path = .externals/awesome-design-md
+	url = https://git.pchuan.top/chuan/awesome-design-md

Cargo.toml

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+[package]
+name = "design"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

README.md

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+# design
+
+一个最基础的 Rust 控制台程序仓库。
+
+## 运行
+
+```bash
+cargo run
+```

src/main.rs

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+fn main() {
+    println!("Hello, design!");
+}