chore: Add a table of contents at the beginning of README.md (#200)

Signed-off-by: Caroline Russell <caroline@appthreat.dev>

README.md

@@ -7,6 +7,37 @@ OWASP dep-scan is a next-generation security and risk audit tool based on known
 [![release](https://github.com/owasp-dep-scan/dep-scan/actions/workflows/pythonpublish.yml/badge.svg)](https://github.com/owasp-dep-scan/dep-scan/actions/workflows/pythonpublish.yml)
 [![Discord](https://img.shields.io/badge/-Discord-lime?style=for-the-badge&logo=discord&logoColor=white&color=black)](https://discord.gg/pF4BYWEJcS)
 
+## Contents
+- [Features](#features)
+    - [Vulnerability Data sources](#vulnerability-data-sources)
+    - [Linux distros](#linux-distros)
+- [Usage](#usage)
+    - [OCI Artifacts via ORAS cli](#oci-artifacts-via-oras-cli)
+    - [Single binary executables](#single-binary-executables)
+    - [Server mode](#server-mode)
+    - [Scanning projects locally (Python version)](#scanning-projects-locally-python-version)
+    - [Scanning containers locally (Python version)](#scanning-containers-locally-python-version)
+    - [Scanning projects locally (Docker container)](#scanning-projects-locally-docker-container)
+- [Supported languages and package format](#supported-languages-and-package-format)
+- [Reachability analysis](#reachability-analysis)
+    - [Example analysis for a Java project](#example-analysis-for-a-java-project)
+    - [Example analysis for a JavaScript project](#example-analysis-for-a-javascript-project)
+- [Customization through environment variables](#customization-through-environment-variables)
+- [GitHub Security Advisory](#github-security-advisory)
+- [Suggest mode](#suggest-mode)
+- [Package Risk audit](#package-risk-audit)
+    - [Automatic adjustment](#automatic-adjustment)
+    - [Configuring weights](#configuring-weights)
+- [Live OS scan](#live-os-scan)
+- [License scan](#license-scan)
+- [Kubernetes and Cloud apps](#kubernetes-and-cloud-apps)
+- [PDF reports](#pdf-reports)
+- [Custom reports](#custom-reports)
+- [Performance tuning](#performance-tuning)
+    - [Use nydus to speed up the initial vdb download](#use-nydus-to-speed-up-the-initial-vdb-download)
+- [Discord support](#discord-support)
+- [License](#license)
+
 ## Features
 
 -   Scan most application code - local repos, Linux container images, Kubernetes manifests, and OS - to identify known CVEs with prioritization