chore(kb/kro): expand a bit

knowledge base/kubernetes/kro.md

@@ -1,47 +1,64 @@
 # Kube Resource Orchestrator
 
-> TODO
-
-Intro
-
-<!-- Remove this line to uncomment if used
-## Table of contents <!-- omit in toc -->
+Allows defining custom Kubernetes APIs using simple and straightforward configuration.
 
 1. [TL;DR](#tldr)
+1. [Create the RDG](#create-the-rdg)
 1. [Further readings](#further-readings)
    1. [Sources](#sources)
 
 ## TL;DR
 
-<!-- Uncomment if used
+Configuring new custom APIs creates a group of Kubernetes objects and the logical operations between them.<br/>
+`kro` calculates the order in which objects should be created based on Common Expression Language expressions.
+
+CLE allows passing values from one object to another, and incorporate conditionals into the custom API definitions.<br/>
+One can define default values for fields in the API specification, allowing end users to invoke custom APIs to create
+grouped resources with minimal configuration.
+
+Installing `kro` in a cluster installs the `ResourceGraphDefinition` Custom Resource Definition.
+
+Custom APIs are created by defining Custom Resources for the `ResourceGraphDefinition` CRD.<br/>
+Those CRs encapsulate the necessary resources, any additional logic, abstractions, and best practices.<br/>
+When the CR is applied to the cluster, it creates a new API of the kind it describes. Users can then create an instance
+of the CR, which will make the custom API handle the deployment and configuration of the required resources.
+
+When creating an RGD, `kro`:
+
+1. Treats resources as a Directed Acyclic Graph to understand their dependencies.
+1. Validates resource definitions and detects the correct deployment order.
+1. Creates a new API in the cluster from the CR.
+1. Configures itself to watch and serve instances of this API, continuously reconciling the resources defined by the
+   RDG.
+
 <details>
   <summary>Setup</summary>
 
 ```sh
+# Install.
+helm --namespace 'kro-system' --create-namespace upgrade --install 'kro' 'oci://registry.k8s.io/kro/charts/kro'
+helm -n 'kro-system' --create-namespace install 'kro' 'oci://registry.k8s.io/kro/charts/kro' --version '0.7.1'
+
+# Uninstall.
+helm -n 'kro-system' uninstall 'kro'
 ```
 
 </details>
--->
 
-<!-- Uncomment if used
-<details>
-  <summary>Usage</summary>
+## Create the RDG
 
-```sh
-```
+1. Create its manifest file.
+1. Apply the RGD to the Kubernetes cluster:
 
-</details>
--->
+   ```sh
+   kubectl apply -f 'resourceGraphDefinition.yaml'
+   ```
 
-<!-- Uncomment if used
-<details>
-  <summary>Real world use cases</summary>
+1. Check the status of the RGD:
 
-```sh
-```
-
-</details>
--->
+   ```sh
+   kubectl get rgd 'myApplication' -o 'wide'
+   ```
 
 ## Further readings