Refer to use-cases in example arch intro

As suggested by editor comment on Appendix A: Use Cases,
we should refer to that appendix where we introduce the
architecture.

Change-Id: I570c9c0cb5a094487da0a19b0f1eb4100909447b
Adds section about Private Flavors

Change-Id: I4d29b7b7c9bfeda9b78ba79442e813df990951ad
Wrangling preface

Based on IRC discussion, this edit attempts to wrangle the preface
into something that makes fair comparisons to other open source-like
private cloud software.

Change-Id: I3fff210b9e802e76823095abda00cd0784255001
Merge "Refer to use-cases in example arch intro"
Merge "Adds section about Private Flavors"
Merge "Wrangling preface"