[core] Add doc about new filename field

docs/site/content/en/docs/how-to/receive-messages/index.md

@@ -154,8 +154,8 @@ Receive events when server or recipient gets the message, read or played it.
 
 ## Files ![](/images/versions/plus.png)
 
-When people send you files - images, voice messages, and documents - WAHA saves it in the file storage.
-In your application you must download it and use it as you want to. You can find the URL in `mediaUrl` field
+When people send you media - images, voice messages, and documents - WAHA saves it in the file storage.
+In your application you must download it and use it as you want to. You can find the URL in `mediaUrl` field.
 
 For example, you can get the webhook like this with `mediaUrl` value (we've skipped other fields):
 
@@ -173,6 +173,21 @@ For example, you can get the webhook like this with `mediaUrl` value (we've skip
 ```
 Then you can use the link to download the file `http://localhost:3000/api/files/true_11111111111@c.us_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.jpg`.
 
+For documents (file attachments) there's also `filename` field with the original file name.
+```json
+{
+  "event": "message",
+  "session": "default",
+  "payload": {
+    "id": "true_11111111111@c.us_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
+    "timestamp": 1667561485,
+    "from": "11111111111@c.us",
+    "mediaUrl": "http://localhost:3000/api/files/true_11111111111@c.us_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.pdf",
+    "filename": "some-file.pdf"
+  }
+}
+```
+
 To configure the url you can use environment variables `WHATSAPP_API_HOSTNAME` and `WHATSAPP_API_PORT`.
 
 By default, WAHA download all files that the account receive.