How to require a single class

Hello,

Thank you very much for this library, it has worked very well.
However, for some projects I don't need all the features it provides.
For example, for a small script I wrote, all I need is the Issue class. There is no documentation about how to require a particular class/component. It would be ideal also to be able to independently install the required parts.

I ended doing this:

```js
const Issue = require( 'github-api/dist/components/Issue' );
```

If there is a better approach I would love to know about it.

Start by reviewing the documented entry point `github-api/dist/components/Issue` and the package's existing usage documentation. Clarify the supported way to require a single component and whether independently installing parts is in scope; done means the documentation explains the approach and its limitations.

索引モデルが issue の本文から書いたものです。