updates docs

Author: juanfriss

docs/Letter.md

@@ -23,7 +23,7 @@ Name | Type | Description | Notes
 **send_date** | **datetime** | A timestamp in ISO 8601 format which specifies a date after the current time and up to 180 days in the future to send the letter off for production. Setting a send date overrides the default [cancellation window](#section/Cancellation-Windows) applied to the mailpiece. Until the `send_date` has passed, the mailpiece can be canceled. If a date in the format `2017-11-01` is passed, it will evaluate to midnight UTC of that date (`2017-11-01T00:00:00.000Z`). If a datetime is passed, that exact time will be used. A `send_date` passed with no time zone will default to UTC, while a `send_date` passed with a time zone will be converted to UTC. | [optional] 
 **extra_service** | **str** | Add an extra service to your letter. See [pricing](https://www.lob.com/pricing/print-mail#compare) for extra costs incurred. | [optional] 
 **tracking_number** | **str, none_type** | The tracking number, if applicable, will appear here when it becomes available. Dummy tracking numbers are not created in test mode. | [optional] 
-**tracking_events** | [**[TrackingEventNormal]**](TrackingEventNormal.md) | Tracking events are not populated for registered or regular (no extra service) letters. | [optional] 
+**tracking_events** | [**[TrackingEventNormal]**](TrackingEventNormal.md) | An array of tracking_event objects ordered by ascending `time`. Will not be populated for letters created in test mode. | [optional] 
 **return_address** | **str** | Specifies the address the return envelope will be sent back to. This is an optional argument that is available if an account is signed up for the return envelope tracking beta, and has `return_envelope`, and `perforated_page` fields populated in the API request. | [optional] 
 **mail_type** | [**MailType**](MailType.md) |  | [optional] 
 **color** | **bool** | Set this key to `true` if you would like to print in color. Set to `false` if you would like to print in black and white. | [optional] 

lob_python/model/letter.py

@@ -388,7 +388,7 @@ def __init__(self, to, _from, date_created, date_modified, id, return_envelope,
             send_date (datetime, type(None)): A timestamp in ISO 8601 format which specifies a date after the current time and up to 180 days in the future to send the letter off for production. Setting a send date overrides the default [cancellation window](#section/Cancellation-Windows) applied to the mailpiece. Until the `send_date` has passed, the mailpiece can be canceled. If a date in the format `2017-11-01` is passed, it will evaluate to midnight UTC of that date (`2017-11-01T00:00:00.000Z`). If a datetime is passed, that exact time will be used. A `send_date` passed with no time zone will default to UTC, while a `send_date` passed with a time zone will be converted to UTC.. [optional] # noqa: E501
             extra_service (str, type(None)): Add an extra service to your letter. See [pricing](https://www.lob.com/pricing/print-mail#compare) for extra costs incurred.. [optional] # noqa: E501
             tracking_number (str, type(None)): The tracking number, if applicable, will appear here when it becomes available. Dummy tracking numbers are not created in test mode.. [optional] # noqa: E501
-            tracking_events (list, type(None)): Tracking events are not populated for registered or regular (no extra service) letters.. [optional] # noqa: E501
+            tracking_events (list, type(None)): An array of tracking_event objects ordered by ascending `time`. Will not be populated for letters created in test mode.. [optional] # noqa: E501
             return_address (str, AddressEditable, type(None)): Specifies the address the return envelope will be sent back to. This is an optional argument that is available if an account is signed up for the return envelope tracking beta, and has `return_envelope`, and `perforated_page` fields populated in the API request.. [optional]  # noqa: E501
             mail_type (MailType, type(None)): [optional] # noqa: E501
             color (bool, type(None)): Set this key to `true` if you would like to print in color. Set to `false` if you would like to print in black and white.. [optional] # noqa: E501