[excel] (External Calls) Adding fetch post sample (#604)

* Adding post sample

* Fix grammar and spacing

Author: AlexJerabek

docs/develop/use-json.md

@@ -203,6 +203,24 @@ interface Transaction {
 
 :::image type="content" source="../images/create-json-console-output.png" alt-text="The console output from the previous script that shows the property values of the object.":::
 
+### Export JSON with `fetch`
+
+Much like importing data with `fetch`, you can send data from your workbook with a similar command. A `POST` command takes any stringified JSON data and sends it to the specified endpoint.
+
+To see this in action, replace the `console.log(transactions);` line in the previous sample with the following code. This issues a `POST` command to a testing server, then reads the data back.
+
+```typescript
+  const response = await fetch('https://jsonplaceholder.typicode.com/posts', {
+    method: 'POST',
+    body: JSON.stringify(transactions),
+    headers: {
+      'Content-type': 'application/json; charset=UTF-8',
+    },
+  });
+  const jsonData: object[] = await response.json();
+  console.log(jsonData);
+```
+
 ### Use a generic object
 
 The previous sample assumes the table header values are consistent. If your table has variable columns, you'll need to create a generic JSON object. The following script shows a script that logs any table as JSON.