Update Troubleshooting docs

Author: colto

TROUBLESHOOTING.md

@@ -13,6 +13,7 @@ If you can't find a solution below, please open an [issue](https://github.com/se
 * [Environment Variables and Your SendGrid API Key](#environment)
 * [Using the Package Manager](#package-manager)
 * [Rails Specifics](#rails-specifics)
+* [Viewing the Request Body](#request-body)
 
 <a name="migrating"></a>
 ## Migrating from v2 to v3
@@ -115,3 +116,14 @@ gem install sendgrid-ruby -v X.X.X
 ## Rails Specifics
 
 - Namespace collision between Rails own `Mail` class and sendgrid class `Mail`. To avoid that issues please use `SendGrid::Mail` instead.
+
+<a name="request-body"></a>
+## Viewing the Request Body
+
+When debugging or testing, it may be useful to exampine the raw request header to compare against the [documented format](https://sendgrid.com/docs/API_Reference/api_v3.html).
+
+You can do this before `response = sg.client.mail._('send').post(request_body: mail.to_json)` like so:
+
+```ruby
+puts mail
+```