chore: implement track by label docs (#30)

* void label docs

* track by label id

Author: j-r-j

docs/trackUsingLabelIdExample.md

@@ -0,0 +1,57 @@
+Track By Label ID
+======================================
+[ShipEngine](www.shipengine.com) allows you to track a package by its ShipEngine label ID. Please see [our docs](https://www.shipengine.com/docs/tracking/track-by-label-id/) to learn more about tracking shipments.
+
+Input Parameters
+-------------------------------------
+
+The `trackUsingLabelId` method requires the ID of the label associated with the shipment you are trying to track.
+
+Output
+--------------------------------
+The `trackUsingLabelId` method returns tracking information associated with the shipment for the given label ID.
+
+Example
+==============================
+```php
+use ShipEngine\ShipEngine;
+use ShipEngine\Message\ShipEngineException;
+
+function trackLabelWithLabelIdDemoFunction() {
+  $client = new ShipEngine('API-Key');
+  try {
+    print_r($client->trackUsingLabelId('se-75492762'));
+  } catch (ShipEngineException $e) {
+    print_r($e -> getMessage());
+  }
+}
+
+trackLabelWithLabelIdDemoFunction();
+```
+
+Example Output
+-----------------------------------------------------
+
+### Tracking Result
+```php
+Array
+(
+    [tracking_number] => 1Z63R0960322853130
+    [tracking_url] => http://wwwapps.ups.com/WebTracking/processRequest?HTMLVersion=5.0&Requester=NES&AgreeToTermsAndConditions=yes&loc=en_US&tracknum=1Z63R0960322853130
+    [status_code] => UN
+    [carrier_code] => ups
+    [carrier_id] => 3
+    [carrier_detail_code] =>
+    [status_description] => Unknown
+    [carrier_status_code] =>
+    [carrier_status_description] => No tracking information available
+    [ship_date] =>
+    [estimated_delivery_date] =>
+    [actual_delivery_date] =>
+    [exception_description] =>
+    [events] => Array
+        (
+        )
+
+)
+```