Added instructions on embedding agent or assistant into a third-party webpage (#4369)

### What problem does this PR solve?


### Type of change

- [x] Documentation Update

docs/references/agent_component_reference/begin.mdx

@@ -41,7 +41,7 @@ You can set global variables within the **Begin** component, which can be either
   - **line**: Accepts a single line of text without line breaks.
   - **paragraph**: Accepts multiple lines of text, including line breaks.
   - **options**: Requires the user to select a value for this variable from a dropdown menu. And you are required to set *at least* one option for the dropdown menu.
-  - **file**: Requires the user to upload one or multiple files from their device.
+  - **file**: Requires the user to upload one or multiple files.
   - **integer**: Accepts an integer as input.
   - **boolean**: Requires the user to toggle between on and off.
 - **Optional**: A toggle indicating whether the variable is optional. 
@@ -62,9 +62,13 @@ As mentioned earlier, the **Begin** component is indispensable for an agent. Sti
 
 No. Files uploaded to an agent as input are not stored in a knowledge base and will not be chunked using RAGFlow's built-in chunk methods. However, RAGFlow's built-in OSR, DLR, and TSR models will still be applied to process the document.
 
-### File size limit for uploaded file
+### How to upload a webpage or file from a URL?
+
+If you set the type of a variable as **file**, your users will be able to upload a file either from their local device or from an accessible URL. For example:
+
+![upload_file](https://github.com/user-attachments/assets/7ad2a352-0807-4b74-b8d1-d09e5cd37997)
+
+### File size limit for an uploaded file
 
 The maximum file size for each uploaded file is determined by the variable `MAX_CONTENT_LENGTH` in `/docker/.env`. It defaults to 128 MB. If you change the default file size, ensure you also update the value of `client_max_body_size` in `/docker/nginx/nginx.conf` accordingly.
 
-
-