Update docs to reference ability to retry headless JS tasks

docs/headless-js-android.md

@@ -66,8 +66,42 @@ service.putExtras(bundle);
 getApplicationContext().startService(service);
 ```
 
-## Caveats
+## Retries
+By default, the headless JS task will not perform any retries. In order to do so, you need to create a `HeadlessJsRetryPolicy` and throw a specfic `Error`. 
+
+`LinearCountingRetryPolicy` is an implementation of `HeadlessJsRetryPolicy` that allows you to specify a maximum number of retries with a fixed delay between each attempt. If that does not suit your needs then you can easily implement your own `HeadlessJsRetryPolicy`. These policies can simply be passed as an extra argument to the `HeadlessJsTaskConfig` constructor, e.g.
+```java
+HeadlessJsRetryPolicy retryPolicy = new LinearCountingRetryPolicy(
+  3, // Max number of retry attempts
+  1000 // Delay between each retry attempt
+);
+
+return new HeadlessJsTaskConfig(
+    "SomeTaskName",
+    Arguments.fromBundle(extras),
+    5000,
+    false,
+    retryPolicy
+  );
+```
+
+A retry attempt will only be made when a specific `Error` is thrown. Inside a headless JS task, you can import the error and throw it when a retry attempt is required.
+
+Example:
+```javascript
+import { HeadlessJsTaskError } from 'HeadlessJsTask';
 
+module.exports = async (taskData) => {
+  const condition = ...;
+  if (!condition) {
+    throw new HeadlessJsTaskError();
+  }
+};
+```
+If you wish all errors to cause a retry attempt, you will need to catch them and throw the above error. 
+
+## Caveats
+- The function passed to `setTimeout` does not always behave as expected. Instead the function is called only when the application is launched again. If you just need to wait, use the retry functionality. 
 - By default, your app will crash if you try to run a task while the app is in the foreground. This is to prevent developers from shooting themselves in the foot by doing a lot of work in a task and slowing the UI. You can pass a fourth `boolean` argument to control this behaviour.
 - If you start your service from a `BroadcastReceiver`, make sure to call `HeadlessJsTaskService.acquireWakeLockNow()` before returning from `onReceive()`.