Fix #191 - improve node-client example

Author: boly38

src/content/docs/api/node-client.mdx

@@ -12,28 +12,51 @@ The Umami node client allows you to send data to Umami on the server side.
 npm install @umami/node
 ```
 
+This command will install api client [npm package](https://www.npmjs.com/package/@umami/node).
+
+Source of this package is located in [umami-software/node](https://github.com/umami-software/node) GitHub repository.
+
 ## Usage
 
 ```js
 import umami from '@umami/node';
 
-umami.init({
+//~ init
+let umamiClient = new umami.Umami({
   websiteId: '50429a93-8479-4073-be80-d5d29c09c2ec', // Your website id
-  hostUrl: 'https://umami.mywebsite.com', // URL to your Umami instance
+  hostUrl: 'https://umami.mywebsite.com' // URL to your Umami instance
+  // ,userAgent // (optional) agent specifications ( OS / Browser / Device )
 });
 
-umami.track({ url: '/home' });
+//~ (optional) identify : update with you own session attributes
+const sessionId = Date.now();
+const identifyOptions = {
+    "attribute": "11.23",
+    "sessionId": sessionId
+}
+umamiClient.identify(identifyOptions);
+
+//~ track a page
+const url = `https://myapp.example.com/home`;
+const title = "title of /home";
+umamiClient.track({url, title});
+
+//~ track an event - an event has a *name*
+umamiClient.track({url, title, "name": "button-click"}, {"color": "red"});
 ```
 
-If using Umami Cloud, you can use `https://cloud.umami.is` as the host URL.
+If you're using Umami Cloud, then you can use `https://cloud.umami.is` as `hostUrl`.
 
-The properties you can send using the `.track` function are:
+As `.track` function first argument, the properties you can send are:
 
 - **hostname**: Hostname of server
 - **language**: Client language (eg. en-US)
 - **referrer**: Page referrer
 - **screen**: Screen dimensions (eg. 1920x1080)
 - **title**: Page title
 - **url**: Page url
-- **name**: Event name (for custom events)
-- **data**: Event data properties
+And to track event:
+- add **name**: Event name
+
+As `.track` function second argument, you can add custom event information :
+- **data**: Event data custom properties