[torch.package][doc] PackageExporter does not have file_structure (#79948)
Summary: found this issue when testing torch.package. also found an open issue https://github.com/pytorch/pytorch/issues/74221. bootstrapping a fix.
Reviewed By: d4l3k
Differential Revision: D37063748
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79948
Approved by: https://github.com/d4l3k
