Provide a better message to the user if they need to enable additional bot intents

In #5, it was noted that forgetting to enable the `SERVER MEMBERS INTENT` results in seemingly unrelated error messages:

```
Failed to update bot's status: sending the message over the websocket failed
```

It would be great if we could identify that the user hasn't enabled a needed intent and warn them about it on startup, along with steps to fix the situation.