Add additional documentation on `packagerConfig.ignore`

### Pre-flight checklist

- [X] I have read the [contribution documentation](https://github.com/electron/forge/blob/main/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [code of conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project uses.
- [X] I have searched the issue tracker for a bug that matches the one I want to file, without success.

### Electron Forge version

7.3.0

### Electron version

29.0.1

### Operating system

window 10

### Last known working Electron Forge version

_No response_

### Expected behavior

Static resources should be packaged correctly and not lost

### Actual behavior

If you use electron-forge to package electron, you will lose .obj static files in the packaged file.

### Steps to reproduce

I added threejs to electron and then I used electron-forge to package electron. However, .obj files will be lost in the packaged files

```
var mtlLoader = new THREE.MTLLoader()
var objLoader = new THREE.OBJLoader()
mtlLoader.setPath('static/Map/obj/')
mtlLoader.load('room1.mtl',function(materials){
materials.preload();
objLoader.setMaterials(materials)
});
objLoader.setPath('static/Map/obj/')
objLoader.load('room1.obj',function(object){
object.traverse(function(child) {
if(child instanceof THREE.Mesh) {
child.material.transparent=true;
child.receiveShadow = true;
child.castShadow = true;
child.material.map = texture;
}
})
object.position.set(-6,-6,6)
object.transparent=true;
object.opacity=0.5
scene.add(object);
renderer.render(scene,camera);
},undefined,function(error){
console.log(error)
});
```

### Additional information

_No response_