Add an example for uploadManyFiles method

[xephtar]

I am using older version of nodejs-storage. I had an issue about uploading many files into custom path. There is no option to upload custom path with using uploadManyFiles method. But I found an issue that solves this. But there is no example implementation to handle the case.

Can you add an example to upload many files into custom path?

[xephtar]

@ddelgrosso1 I created the issue 🙏

[ddelgrosso1]

Thanks @xephtar!