Write a simple file.

gongor.rs

@@ -1,3 +1,8 @@
-fn main() {
-    println!("Hello World!");
+use std::fs::File;
+use std::io::prelude::*;
+
+fn main() ->  std::io::Result<()>{
+    let mut file = File::create("foo.txt")?;
+    file.write_all(b"Hello, world!")?;
+    Ok(())
 }