Update documentation and example (close #59) (#60)

Author: naskya

README.md

@@ -12,7 +12,8 @@ reference [this excellent document.](https://web.dev/notifications/)
 
 ## Requirements
 
-Clients require an async executor. System Openssl is needed for compilation.
+- Clients require an async executor.
+- OpenSSL is required for compilation. You must install it on your host or use the `vendored` feature of the [openssl](https://docs.rs/openssl/) crate.
 
 ## Migration notes
 
@@ -24,7 +25,6 @@ Example
 
 ```rust
 use web_push::*;
-use web_push::clients::isahc_client::IsahcWebPushClient;
 use std::fs::File;
 
 #[tokio::main]

examples/simple_send.rs

@@ -82,8 +82,11 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>
 
     let client = IsahcWebPushClient::new()?;
 
-    let response = client.send(builder.build()?).await?;
-    println!("Sent: {:?}", response);
+    let result = client.send(builder.build()?).await;
+
+    if let Err(error) = result {
+        println!("An error occured: {:?}", error);
+    }
 
     Ok(())
 }