Add Routing Traffic to Your Application Guide (nginx#991)

Problem: As a potential user of NKG, I want a guide to help me 
understand how to host an application API with NKG so that 
I can easily understand how to start using NKG in my environment 
immediately.

Solution: Add a use case guide that describes how to route all 
traffic to a single application running in Kubernetes using NKG.

Author: miledxz

.gitignore

@@ -33,3 +33,6 @@ node_modules/
 
 # JS test coverage
 internal/mode/static/nginx/modules/coverage
+
+# MacOS Finder
+.DS_Store

docs/guides/README.md

@@ -4,6 +4,8 @@ This directory contains guides for configuring NGINX Kubernetes Gateway for vari
 
 ## Contents
 
+- [Routing Traffic to Your Application](routing-traffic-to-your-app.md): How to use NGINX Kubernetes Gateway to route
+  all Ingress traffic to your Kubernetes application.
 - [Securing Traffic using Let's Encrypt and Cert-Manager](integrating-cert-manager.md): Shows how to secure
   traffic from clients to NGINX Kubernetes Gateway with TLS using Let's Encrypt and Cert-Manager.
 - [Using NGINX Kubernetes Gateway to Upgrade Applications without Downtime](upgrade-apps-without-downtime.md):