Moved registry docs to registry subdirectory

docs/storage-drivers/inmemory.md

@@ -0,0 +1,23 @@
+<!--[metadata]>
++++
+title = "In-memory storage driver"
+description = "Explains how to use the in-memory storage drivers"
+keywords = ["registry, service, driver, images, storage,  in-memory"]
+[menu.main]
+parent="smn_storagedrivers"
++++
+<![end-metadata]-->
+
+
+# In-memory storage driver (Testing Only)
+
+For purely tests purposes, you can use the `inmemory` storage driver. This
+driver is an implementation of the `storagedriver.StorageDriver` interface which
+uses local memory for object storage. If you would like to run a registry from
+volatile memory, use the [`filesystem` driver](filesystem.md) on a ramdisk.
+
+**IMPORTANT**: This storage driver *does not* persist data across runs. This is why it is only suitable for testing. *Never* use this driver in production.
+
+## Parameters
+
+None