Merge pull request #253 from delapuente/add-extra-headers-section-in-readme

Adding headers key to options description.

Author: marco-c

README.md

@@ -85,7 +85,7 @@ const convertedVapidKey = urlBase64ToUint8Array(vapidPublicKey);
 
 registration.pushManager.subscribe({
   userVisibleOnly: true,
-  applicationServerKey: convertedVapidKey  
+  applicationServerKey: convertedVapidKey
 });
 ```
 
@@ -129,7 +129,10 @@ const options = {
     publicKey: '< URL Safe Base64 Encoded Public Key >',
     privateKey: '< URL Safe Base64 Encoded Private Key >'
   },
-  TTL: <Number>
+  TTL: <Number>,
+  headers: {
+    '< header name >': '< header value >'
+  }
 }
 
 webpush.sendNotification(
@@ -175,6 +178,7 @@ request only. This overrides any API key set via `setGCMAPIKey()`.
 *privateKey* values defined. These values should follow the [VAPID Spec](https://tools.ietf.org/html/draft-thomson-webpush-vapid).
 - **TTL** is a value in seconds that describes how long a push message is
 retained by the push service (by default, four weeks);
+- **headers** is an object with all the extra headers you want to add to the request.
 
 ### Returns