readme: Add a section about architecture

README.md

@@ -8,6 +8,47 @@
 
 The sector-storage project provides a implementation-nonspecific reference implementation of the [specs-storage](https://github.com/filecoin-project/specs-storage) interface.
 
+## Architecture
+
+![high-level architecture](docs/sector-storage.svg)
+
+### `Manager`
+
+Manages is the top-level piece of the storage system gluing all the other pieces
+together. It also implements scheduling logic.
+
+### `package stores`
+
+This package implements the sector storage subsystem. Fundamentally the storage
+is divided into `path`s, each path has it's UUID, and stores a set of sector
+'files'. There are currently 3 types of sector files - `unsealed`, `sealed`,
+and `cache`.
+
+Paths can be shared between nodes by sharing the underlying filesystem.
+
+### `stores.Local`
+
+The Local store implements SectorProvider for paths mounted in the local
+filesystem. Paths can be shared between nodes, and support shared filesystems
+such as NFS.
+
+stores.Local implements all native filesystem-related operations 
+
+### `stores.Remote`
+
+The Remote store extends Local store, handles fetching sector files into a local
+store if needed, and handles removing sectors from non-local stores.
+
+### `stores.Index`
+
+The Index is a singleton holding metadata about storage paths, and a mapping of
+sector files to paths
+
+### `LocalWorker`
+
+LocalWorker implements the Worker interface with ffiwrapper.Sealer and a
+store.Store instance
+
 ## License
 
 The Filecoin Project is dual-licensed under Apache 2.0 and MIT terms: