docs: improve signed event webhook validation docs (#1013)

Author: shwetha-manvinkurke

TROUBLESHOOTING.md

@@ -15,6 +15,7 @@ If you can't find a solution below, please open an [issue](https://github.com/se
 * [Version Convention](#versions)
 * [Viewing the Request Body](#request-body)
 * [Error Handling](#error-handling)
+* [Verifying Event Webhooks](#signed-webhooks)
 
 <a name="environment"></a>
 ## Environment Variables and Your Twilio SendGrid API Key
@@ -117,3 +118,14 @@ You can do this right before you call `response = sg.client.mail.send.post(reque
 # Error Handling
 
 Please review [our use_cases](use_cases/README.md) for examples of error handling.
+
+<a name="signed-webhooks"></a>
+## Signed Webhook Verification
+
+Twilio SendGrid's Event Webhook will notify a URL via HTTP POST with information about events that occur as your mail is processed. [This](https://docs.sendgrid.com/for-developers/tracking-events/getting-started-event-webhook-security-features) article covers all you need to know to secure the Event Webhook, allowing you to verify that incoming requests originate from Twilio SendGrid. The sendgrid-python library can help you verify these Signed Event Webhooks.
+
+You can find the usage example [here](examples/helpers/eventwebhook/eventwebhook_example.py) and the tests [here](test/test_eventwebhook.py). 
+If you are still having trouble getting the validation to work, follow the following instructions:
+- Be sure to use the *raw* payload for validation
+- Be sure to include a trailing carriage return and newline in your payload
+- In case of multi-event webhooks, make sure you include the trailing newline and carriage return after *each* event