add doc about cc blobstore staging interactions
add doc about cc blobstore staging interactions

* TODO: talk about expiry
* TODO: extract resource matching load into its own section
* TODO: talk about versioning
* TODO: list default operation timeouts (and where to find them)

[https://www.pivotaltracker.com/story/show/165781280]

Authored-by: Connor Braa <e624947c8d30070ca3f5f65daa9bdf76de21947b@pivotal.io>

cloudfoundry/docs-cloudfoundry-concepts