Expand example rate request comment on the use of GroupPackageCount to indicate possible use-case.
Expand example rate request comment on the use of GroupPackageCount to
indicate possible use-case.

python-fedex-devs/python-fedex,gtaylor/python-fedex,python-fedex-devs/python-fedex,gtaylor/python-fedex,obr/python-fedex,gtaylor/python-fedex,gtaylor/python-fedex,obr/python-fedex,python-fedex-devs/python-fedex,python-fedex-devs/python-fedex