Add missing .await? to README

http-signature-normalization-actix/README.md

@@ -38,6 +38,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .authorization_signature_with_digest(&config, "my-key-id", &mut digest, "Hewwo-owo", |s| {
             Ok(base64::encode(s)) as Result<_, MyError>
         })?
+        .await?
         .send()
         .await
         .map_err(|e| {