s/Zwift/ZeroCloud/g

Zwift is a deprecated term for Swift+ZeroVM. ZeroCloud is the preferred
nomenclature.
Merge pull request #95 from larsbutler/rename-zwift-zerocloud

Replace "Zwift" with "ZeroCloud"
doc: add zerocloud auth config guide

This adds auth config documentation for both v1 and v2 auth schemes for
Swift/ZeroCloud.