docs: Adds example to review request body for troubleshooting.

TROUBLESHOOTING.md

@@ -0,0 +1,30 @@
+If you have a non-library SendGrid issue, please contact our [support team](https://support.sendgrid.com).
+
+If you can't find a solution below, please open an [issue](https://github.com/sendgrid/nodejs-http-client/issues).
+
+## Table of Contents
+* [Viewing the Request Body](#request-body)
+
+<a name="request-body"></a>
+## Viewing the Request Body
+
+When debugging or testing, it may be useful to examine the raw request body to compare against the [documented format](https://sendgrid.com/docs/API_Reference/api_v3.html).
+
+You can do this with something like:
+```javascript
+var requestPost = client.emptyRequest()
+requestPost.method = 'POST'
+requestPost.path = '/v3/api_keys'
+requestPost.body = { data: 'some test data' }
+requestPost.headers['X-Test'] = 'test'
+
+// Log request body before sending POST request.
+console.log(requestPost.body)
+
+client.API(requestPost, (response) => {
+  // Log the response.
+  console.log(response.statusCode)
+  console.log(response.body)
+  console.log(response.headers)
+})
+```