Implement Some Tokio Tutorials

Tutorial/WritePart.rs

@@ -0,0 +1,16 @@
+#![allow(non_snake_case)]
+
+use tokio::fs::File;
+use tokio::io::{self, AsyncWriteExt};
+
+#[tokio::main]
+async fn main() -> io::Result<()> {
+    let mut file = File::create("File.txt").await?;
+
+    // Writes some prefix of the byte string, but not necessarily all of it.
+    let n = file.write(b"some bytes").await?;
+
+    println!("Wrote the first {} bytes of 'some bytes'.", n);
+
+    Ok(())
+}