docs(index.md): improve styling

docs/index.md

@@ -2,24 +2,35 @@
 
 The documentation is divided into the following sections:
 
+## Introduction
+
 - [Introduction](introduction.md)
-  - [What is Kube-router?](introduction.md#what-is-kube-router)
-  - [Why Kube-router?](introduction.md#why-kube-router)
-- Concepts
-  - [See it in action](see-it-in-action.md)
-  - [How it works?](how-it-works.md)
-  - [Architecture](architecture.md)
+- [What is Kube-router?](introduction.md#what-is-kube-router)
+- [Why Kube-router?](introduction.md#why-kube-router)
+
+## Concepts
+
+- [See it in action](see-it-in-action.md)
+- [How it works?](how-it-works.md)
+- [Architecture](architecture.md)
+
+## User Guide
+
 - [User Guide](user-guide.md)
-  - [installation](user-guide.md#try-kube-router-with-cluster-installers)
-  - [requirements](user-guide.md#requirements)
-- Operations guide
-  - [Health](health.md)
-  - [Observability](observability.md)
-  - [Troubleshooting](troubleshoot.md)
-  - [Pod toolbox](pod-toolbox.md)
-  - [Upgrades](upgrading.md)
-  - [IPv6 / Dual-Stack](ipv6.md)
-  - [Load Balancer Support](load-balancer-allocator.md)
-- Developer and Contributor Guide
-  - [Developer Guide](developing.md)
-  - [Contributor Guideline](/CONTRIBUTING.md)
+- [installation](user-guide.md#try-kube-router-with-cluster-installers)
+- [requirements](user-guide.md#requirements)
+
+## Operations guide
+
+- [Health](health.md)
+- [Observability](observability.md)
+- [Troubleshooting](troubleshoot.md)
+- [Pod toolbox](pod-toolbox.md)
+- [Upgrades](upgrading.md)
+- [IPv6 / Dual-Stack](ipv6.md)
+- [Load Balancer Support](load-balancer-allocator.md)
+
+## Developer and Contributor Guide
+
+- [Developer Guide](developing.md)
+- [Contributor Guideline](/CONTRIBUTING.md)