feat: added examples

examples/basic.rs

@@ -0,0 +1,15 @@
+use envkit::EnvLoader;
+
+fn main() -> Result<(), envkit::error::EnvError> {
+    let loader = EnvLoader;
+
+    let port: u16 = loader.get("PORT")?;
+    let debug: bool = loader.get_or("DEBUG", false);
+    let app_name: String = loader.get_opt("APP_NAME").unwrap_or_else(|| "envkit".to_string());
+
+    println!("port={port}");
+    println!("debug={debug}");
+    println!("app_name={app_name}");
+
+    Ok(())
+}