Add README for docs directory (nginx#968)

Author: miledxz

docs/README.md

@@ -0,0 +1,24 @@
+# NGINX Kubernetes Gateway Documentation
+
+This directory contains all of the documentation relating to NGINX Kubernetes Gateway.
+
+## Contents
+
+- [Architecture](architecture.md): An overview of the architecture and design principles of NGINX Kubernetes Gateway.
+- [Gateway API Compatibility](gateway-api-compatibility.md): Describes which Gateway API resources NGINX Kubernetes
+Gateway supports and the extent of that support.
+- [Installation](installation.md): Walkthrough on how to install NGINX Kubernetes Gateway on a generic Kubernetes cluster.
+- [Resource Validation](resource-validation.md): Describes how NGINX Kubernetes Gateway validates Gateway API
+resources.
+- [Control Plane Configuration](control-plane-configuration.md): Describes how to dynamically update the NGINX
+Kubernetes Gateway control plane configuration.
+- [Building the Images](building-the-images.md): Steps on how to build the NGINX Kubernetes Gateway container images
+yourself.
+- [Running on Kind](running-on-kind.md): Walkthrough on how to run NGINX Kubernetes Gateway on a `kind` cluster.
+- [CLI Help](cli-help.md): Describes the commands available in the `gateway` binary of `nginx-kubernetes-gateway`
+container.
+
+### Directories
+
+- [Developer](developer/): Docs for developers of the project. Contains guides relating to processes and workflows.
+- [Proposals](proposals/): Enhancement proposals for new features.