Moved registry docs to registry subdirectory

docs/storage-drivers/index.md

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+<!--[metadata]>
++++
+title = "Storage Driver overview"
+description = "Explains how to use storage drivers"
+keywords = ["registry, on-prem, images, tags, repository, distribution, storage drivers, advanced"]
+aliases = ["/registry/storagedrivers/"]
+[menu.main]
+parent="smn_storagedrivers"
+identifier="storage_index"
+weight=-1
++++
+<![end-metadata]-->
+
+
+# Docker Registry Storage Driver
+
+This document describes the registry storage driver model, implementation, and explains how to contribute new storage drivers.
+
+## Provided Drivers
+
+This storage driver package comes bundled with several drivers:
+
+- [inmemory](inmemory.md): A temporary storage driver using a local inmemory map. This exists solely for reference and testing.
+- [filesystem](filesystem.md): A local storage driver configured to use a directory tree in the local filesystem.
+- [s3](s3.md): A driver storing objects in an Amazon Simple Storage Solution (S3) bucket.
+- [azure](azure.md): A driver storing objects in [Microsoft Azure Blob Storage](http://azure.microsoft.com/en-us/services/storage/).
+- [swift](swift.md): A driver storing objects in [Openstack Swift](http://docs.openstack.org/developer/swift/).
+- [oss](oss.md): A driver storing objects in [Aliyun OSS](http://www.aliyun.com/product/oss).
+- [gcs](gcs.md): A driver storing objects in a [Google Cloud Storage](https://cloud.google.com/storage/) bucket.
+
+## Storage Driver API
+
+The storage driver API is designed to model a filesystem-like key/value storage in a manner abstract enough to support a range of drivers from the local filesystem to Amazon S3 or other distributed object storage systems.
+
+Storage drivers are required to implement the `storagedriver.StorageDriver` interface provided in `storagedriver.go`, which includes methods for reading, writing, and deleting content, as well as listing child objects of a specified prefix key.
+
+Storage drivers are intended to be written in Go, providing compile-time
+validation of the `storagedriver.StorageDriver` interface.
+
+## Driver Selection and Configuration
+
+The preferred method of selecting a storage driver is using the `StorageDriverFactory` interface in the `storagedriver/factory` package. These factories provide a common interface for constructing storage drivers with a parameters map. The factory model is based off of the [Register](http://golang.org/pkg/database/sql/#Register) and [Open](http://golang.org/pkg/database/sql/#Open) methods in the builtin [database/sql](http://golang.org/pkg/database/sql) package.
+
+Storage driver factories may be registered by name using the
+`factory.Register` method, and then later invoked by calling `factory.Create`
+with a driver name and parameters map. If no such storage driver can be found,
+`factory.Create` will return an `InvalidStorageDriverError`.
+
+## Driver Contribution
+
+### Writing new storage drivers
+
+To create a valid storage driver, one must implement the
+`storagedriver.StorageDriver` interface and make sure to expose this driver
+via the factory system.
+
+#### Registering
+
+Storage drivers should call `factory.Register` with their driver name in an `init` method, allowing callers of `factory.New` to construct instances of this driver without requiring modification of imports throughout the codebase.
+
+## Testing
+
+Storage driver test suites are provided in
+`storagedriver/testsuites/testsuites.go` and may be used for any storage
+driver written in Go. Tests can be registered using the `RegisterSuite`
+function, which run the same set of tests for any registered drivers.