No description of the configuration

The documentation seems to lack any description of what the `$config` variable should contain.

[The installation docs](https://botman.io/2.0/installation) under 'Basic Usage without BotMan Studio' stipulate a `$config` variable, and define it as an array, but not any of the keys.

```php
$config = [
// Your driver-specific configuration
// "telegram" => [
// "token" => "TOKEN"
// ]
];
```

The 'driver-specific configuration' seems to suggest this would be in the driver. However all I could find [was the root array key for the driver](https://github.com/botman/driver-hipchat/blob/master/src/HipChatDriver.php#L29), but not what any of the configuration key values were.

The `BotMan` class which takes the `$config` variable [does not type hint `$config` as an array](https://github.com/botman/botman/blob/2.0/src/BotMan.php#L129), so I'm not sure if it has to be an array or not.

My specific use-case is that I'm trying to configure Hipchat, and the [documentation for this driver does not detail any of the configuration required](https://botman.io/2.0/driver-hipchat#installation-setup).

So I feel at a bit of a dead-end here. This leads me to think there could be some improvements to the documentation made, for those of us who are not using BotMan Studio, or paying for the video course.

Start with the “Basic Usage without BotMan Studio” section in the installation docs and the HipChat driver installation page. Compare their `$config` examples with the configuration access in the linked HipChatDriver.php and the `$config` handling in BotMan.php. Done means the documentation explains the expected structure and driver-specific keys, including a usable HipChat configuration example.

Written by the indexing model from the issue text.