Add Table of Contents to README.md

This update introduces a comprehensive Table of Contents to the README.md file. It enhances navigation and makes it easier for users to find relevant sections quickly.

README.md

@@ -7,6 +7,21 @@
 NexaPG is a full-stack PostgreSQL monitoring platform for multiple remote targets.
 It combines FastAPI, React, and PostgreSQL in a Docker Compose stack with RBAC, polling collectors, query insights, alerting, and target-owner email notifications.
 
+## Table of Contents
+
+- [Quick Start](#quick-start)
+- [Prerequisites](#prerequisites)
+- [Make Commands](#make-commands)
+- [Configuration Reference (`.env`)](#configuration-reference-env)
+- [Core Functional Areas](#core-functional-areas)
+- [Target Owner Notifications](#target-owner-notifications)
+- [API Overview](#api-overview)
+- [`pg_stat_statements` Requirement](#pg_stat_statements-requirement)
+- [Reverse Proxy / SSL Guidance](#reverse-proxy--ssl-guidance)
+- [PostgreSQL Compatibility Smoke Test](#postgresql-compatibility-smoke-test)
+- [Troubleshooting](#troubleshooting)
+- [Security Notes](#security-notes)
+
 ## Highlights
 
 - Multi-target monitoring for remote PostgreSQL instances