reorganized the directories

projects/clippy_demo/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "clippy_demo"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

projects/clippy_demo/src/main.rs

@@ -0,0 +1,5 @@
+fn main() {
+    let x = std::f64::consts::PI;
+    let r = 8.0;
+    println!("圆的面积为 {}", x * r * r);
+}