update internal package readme
This directory contains packages which are internally used in shinpuru.
- [`commands`](commands/): All Discord command definitions loaded by [shireikan](https://github.com/zekrotja/shireikan).
-- [`config`](config/): The definition of the config stucture and available loaders for different file formats.
- [`inits`](inits/): Functions used to wrap initialization procedures of services so that they can be used on service registration in a simple and clean way.
- [`listeners`](listeners/): All registered listeners for Discord events.
- [`middleware`](middleware/): Command middlewares registered by [shireikan](https://github.com/zekrotja/shireikan) to check permission, rate limit and log on command execution.
