docs: add logging start to readme example.

Refs: #651
Refs: #656

Author: Fishrock123

README.md

@@ -60,6 +60,7 @@ async-std = { version = "1.6.0", features = ["attributes"] }
 ```rust
 #[async_std::main]
 async fn main() -> Result<(), std::io::Error> {
+    tide::log::start();
     let mut app = tide::new();
     app.at("/").get(|_| async { Ok("Hello, world!") });
     app.listen("127.0.0.1:8080").await?;