docs: update generator-template.md for AsyncAPI v3 parser usage

apps/generator/docs/generator-template.md

@@ -9,7 +9,7 @@ Suppose you can only sleep when the AC in your bedroom is set to 22 °C, and you
 
 In this tutorial:
 
-- You'll use the [Eclipse Mosquito](https://test.mosquitto.org) **MQTT broker**, which you'll connect to subscribe and publish messages using an MQTT client.
+- You'll use the [Eclipse Mosquitto](https://test.mosquitto.org) **MQTT broker**, which you'll connect to subscribe and publish messages using an MQTT client.
 - You'll use [Python Paho-MQTT](https://pypi.org/project/paho-mqtt/) as the **MQTT client** in this project.
 - You'll create a React template that will use the MQTT broker to allow you to monitor your bedroom's temperature and notify you when the temperature drops or rises above 22 °C.
 - Lastly, create a reusable component for the output code's `sendTemperatureDrop` and `sendTemperatureRise` functions.
@@ -39,45 +39,77 @@ Before you begin, make sure you have the following set up:
 
 ## Background context
 
-There is a list of [community maintained templates](https://www.asyncapi.com/docs/tools/generator/template#generator-templates-list), but what if you do not find what you need? In that case, you'll create a user-defined template that generates custom output from the generator.
-Before you create the template, you'll need to have an [AsyncAPI document](https://www.asyncapi.com/docs/tools/generator/asyncapi-document) that defines the properties you want to use in your template to test against. In this tutorial, you'll use the following template saved in the **test/fixtures/asyncapi.yml** file in your template project directory.
+**This tutorial focuses on code generation using templates — not full AsyncAPI document modeling.**
 
-``` yml
+There is a list of [community maintained templates](https://www.asyncapi.com/docs/tools/generator/template#generator-templates-list), but what if you do not find what you need? In that case, you'll create a user-defined template that generates custom output from the generator.
+Before you create the template, you'll need an [AsyncAPI document](https://www.asyncapi.com/docs/tools/generator/asyncapi-document) that defines the properties used in your generator. This tutorial focuses on code generation using templates — not full AsyncAPI document modeling.
+In this tutorial, we use a simplified AsyncAPI document focused on extracting data for template generation.
+You'll use the following document saved as test/fixtures/asyncapi.yml.
 
-asyncapi: 2.6.0
+> 🧭 **Note on AsyncAPI v3 semantics:**  
+> In AsyncAPI v3, the meaning of `publish` and `subscribe` has changed from v2. Now, `action: send` under the top-level `operations` object indicates that the application is publishing (i.e., sending) the message. This tutorial uses that new approach.
 
+```yaml
+asyncapi: 3.0.0
 info:
   title: Temperature Service
   version: 1.0.0
-  description: This service is in charge of processing all the events related to temperature.
+  description: Service that emits temperature changes from a bedroom sensor.
 
 servers:
+  production:
+    host: broker.example.com
   dev:
     url: test.mosquitto.org #in case you're using local mosquitto instance, change this value to localhost.
     protocol: mqtt
 
 channels:
-  temperature/changed:
-    description: Updates the bedroom temperature in the database when the temperatures drops or goes up.
-    publish:
-      operationId: temperatureChange
-      message:
-        description: Message that is being sent when the temperature in the bedroom changes.
+  temperatureChanged:
+    address: temperature/changed
+    messages:
+      temperatureChange:
+        description: Message sent when the temperature in the bedroom changes.
         payload:
-          type: object
-          additionalProperties: false
-          properties:
-            temperatureId:
-              type: string
+          $ref: '#/components/schemas/Temperature' # refactored from inline payload for better reuse
+
+operations:
+  sendTemperatureChanged:
+    action: send
+    summary: Temperature changes are pushed to the broker
+    channel:
+      $ref: '#/channels/temperatureChanged'
+
 components:
   schemas:
-    temperatureId:
+    Temperature:
       type: object
       additionalProperties: false
       properties:
-        temperatureId:
+        value:
+          type: number
+        unit:
           type: string
+
 ```
+> 🛠️ **Note on Payload Schema Refactor:**  
+> The payload was previously inline with a field like temperatureId. In this version, it’s refactored into a reusable Temperature schema component. While the field names were also cleaned up (temperatureId → value, unit), the functional meaning remains unchanged. This aligns with AsyncAPI v3's best practices for reuse and separation of concerns. Only the naming changed (temperatureId → value) to more clearly match the data's purpose. This is purely cosmetic and doesn’t affect function.
+
+> 🆕 This document uses the AsyncAPI 3.0.0 structure. Notable changes include `operations` now being top-level and the use of `address:` in `channels` instead of nested publish/subscribe.
+
+## Handling Diagnostics (Warnings)
+
+When using the latest AsyncAPI parser, it's important to handle not just errors but also diagnostics (warnings). These help identify non-critical issues, such as missing recommended fields like `license`, `contact`, or outdated spec versions.
+
+```ts
+const { parseFromFile } = require('@asyncapi/parser');
+
+const result = await parseFromFile('example-asyncapi.yaml');
+
+if (result.diagnostics && result.diagnostics.length > 0) {
+  console.warn('⚠️ Found diagnostics:');
+  console.dir(result.diagnostics, { depth: null });
+}
+
 
 ## Overview of steps
 
@@ -100,7 +132,7 @@ python-mqtt-client-template
 └── package.json
 ```
 
-Lets break it down:
+Let's break it down:
 
 ### package.json file