Update src/README.md.

src/README.md

@@ -26,6 +26,13 @@ Implements abstract methods for writer allocation and metadata.
 Specifically, `ZarrV2` allocates one writer of type `ChunkWriter` for each multiscale level-of-detail
 and writes metadata in the format specified by the [Zarr V2 spec](https://zarr.readthedocs.io/en/stable/spec/v2.html).
 
+### The `ZarrV3` class
+
+Subclass of the `Zarr` class.
+Implements abstract methods for writer allocation and metadata.
+Specifically, `ZarrV3` allocates one writer of type `ShardWriter` for each multiscale level-of-detail
+and writes metadata in the format specified by the [Zarr V3 spec](https://zarr-specs.readthedocs.io/en/latest/specs.html).
+
 ### The `Writer` class
 
 An abstract class that writes frames to the filesystem or other storage layer.
@@ -36,6 +43,15 @@ The `Writer` handles chunking, chunk compression, and writing.
 
 Subclass of the `Writer` class.
 Implements abstract methods relating to writing and flushing chunk buffers.
+Chunk buffers, whether raw or compressed, are written to individual chunk files. 
+
+### The `ShardWriter` class
+
+Subclass of the `Writer` class.
+Implements abstract methods relating to writing, sharding, and flushing chunk buffers.
+Chunk buffers, whether raw or compressed, are concatenated into shards, which are written out to individual shard files.
+
+
 
 ### The `BloscCompressionParams` struct