Clarify error message when failing to forward WebSocket events

[Xemdo]

What is the problem?

When running an event that should forward to a WebSocket server, a vague error message will appear:

> twitch event trigger channel.update --transport=websocket --version 2
Failed to dial RPC handler for WebSocket server. Is it online?
Error: dial tcp :44747: connectex: No connection could be made because the target machine actively refused it.

This should be clarified to indicate what command to run to start the server.

Operating System

All

Architecture Version (x86, x64, arm, etc)

All

Steps to reproduce

twitch event trigger <any event> --transport=websocket

Relevant log output

No response