Document SQL database usage, manifest properties, and migration
Document SQL database usage, manifest properties, and migration

[finishes #131103477]

Signed-off-by: Swetha Repakula <a5734a87406f5f357b62e206d655a02a4f6ee691@us.ibm.com>
Signed-off-by: Chris Piraino <f047703f03f13cc8e1b226aa8ba85c2dfc238f94@pivotal.io>

cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release