Adds swift object versioning to End User Guide

With the moving of the Object Storage API content from a
long-form dev guide to a specification, some topics needed
To be added to the End User Guide.

Change-Id: I2b6179bec34e1ebaa7f4678f43f69385691c615b
Partial-bug: 1392382
Merge "Adds swift object versioning to End User Guide"