docs(psk2): add table of contents

0024-pre-shared-key-v2/0024-pre-shared-key-v2.md

@@ -6,13 +6,30 @@ draft: 1
 
 This spec defines version 2 of the Pre-Shared Key Transport Protocol. PSKv2 implements end-to-end data encryption, condition and fulfillment generation, [End-to-End Quoting](#end-to-end-quoting) and [Chunked Payments](#chunked-payments). The approach to chunked payments is inspired by the Internet's Transmission Control Protocol (TCP).
 
+**Table of Contents**
+
+* [Overview](#overview)
+  + [Setup](#setup)
+  + [Encryption](#encryption)
+  + [Condition and Fulfillment Generation](#condition-and-fulfillment-generation)
+  + [End-To-End Quoting](#end-to-end-quoting)
+  + [Chunked Payments](#chunked-payments)
+* [Model of Operation](#model-of-operation)
+  + [Informational Quote](#informational-quote)
+  + [Single Payment](#single-payment)
+  + [Chunked Payment](#chunked-payment)
+* [Specification](#specification)
+  + [Encryption](#encryption-1)
+  + [Data Packet](#data-packet)
+* [Appendix A: Advanced Sender Features](#appendix-a-advanced-sender-features)
+
 ## Overview
 
 Like [PSKv1](./0016-pre-shared-key/0016-pre-shared-key.md), PSKv2 uses a secret shared between the sender and receiver to generate the conditions and fulfillments for payments without repeated end-to-end communication. PSKv2 additionally includes support for End-to-End Quoting and Chunked Payments.
 
 This specificiation aims to standardize the behavior of receivers while allowing for sophisticated sender behavior to be developed in the future. [Appendix A: Advanced Sender Features](#appendix-a-advanced-sender-features) outlines areas for potential sender features to be implemented in the future.
 
-## Setup
+### Setup
 
 Before using PSKv2, the sender and receiver use an authenticated, encrypted communication channel (generally provided as part of an [Application Layer Protocol](./0001-interledger-architecture/0001-interledger-architecture.md#application-layer)) to exchange: