1774 extensibility v1 create an exhaustive documentation readme or dedicated section in twenty contributing doc (#16751)

As title

<img width="1108" height="894" alt="image"
src="https://github.com/user-attachments/assets/e2dc7e12-72e3-4ca3-ac7b-a94de547f82a"
/>

packages/twenty-cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "twenty-cli",
-  "version": "0.3.0",
+  "version": "0.3.1",
   "description": "[DEPRECATED] Use twenty-sdk instead: https://www.npmjs.com/package/twenty-sdk",
   "scripts": {
     "build": "echo 'use npx nx build'",