[docs] Document Django Channels WebSocket endpoints

[nemesifier]

Document Django Channels WebSocket API

Context: This repository provides a Django Channels WebSocket endpoint for live notifications:

• Notification updates: ws://<host>/ws/notification/

There is no explicit user-facing documentation describing the WebSocket endpoints or their message types.

Message Types

• notification (with various fields)

Suggestion:
Please create documentation in docs/user/websocket-api.rst (or similar location) covering:

• Connection URL and message types
• Authentication/authorization requirements
• Example payloads
• Purpose: Help developers integrate notifications and clarify API boundaries

This is modeled after the suggestion in openwisp-firmware-upgrader.