Clarify that you should use JSON body for parameters (#34)

Author: bcherry

TEMPLATE.md

@@ -12,9 +12,10 @@ When running this token server as a sandbox app, LiveKit hosts a public endpoint
 | ------------------ | ---------------------------- | ------------------------------ |
 | Method             | `POST`                       |                                |
 | URL                | `https://cloud-api.livekit.io/api/sandbox/connection-details` |
-| Query Parameters   | `roomName` (optional)        | (your room name)               |
-|                    | `participantName` (optional) | (your participant name)        |
+| Optional Parameters| `roomName`                   | (your room name)               |
+|                    | `participantName`            | (your participant name)        |
 | Headers            | `X-Sandbox-ID`               | (your Sandbox ID)              |
+|                    | `Content-Type`               | `application/json`             |
 
 Generated tokens will have a default TTL of 15 minutes. Optional parameters not included in the request will be generated by the token server.