docs: improve signed webhook event validation docs (#472)

Author: shwetha-manvinkurke

TROUBLESHOOTING.md

@@ -17,6 +17,7 @@ If you can't find a solution below, please open an [issue](https://github.com/se
 * [Rails Specifics](#rails-specifics)
 * [Ruby Versions](#ruby-versions)
 * [Viewing the Request Body](#viewing-the-request-body)
+* [Verifying Event Webhooks](#signed-webhooks)
 
 <a name="migrating"></a>
 ## Migrating from v2 to v3
@@ -137,3 +138,14 @@ You can do this before `response = sg.client.mail._('send').post(request_body: m
 ```ruby
 puts mail.to_json
 ```
+
+<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-ruby library can help you verify these Signed Event Webhooks.
+
+You can find the usage example [here](examples/helpers/eventwebhook/example.rb) and the tests [here](spec/sendgrid/helpers/eventwebhook/eventwebhook_spec.rb). 
+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