Add garbage collection release notes

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

releases/v1.0.0-beta.3.toml

@@ -28,6 +28,24 @@ Most notably:
 - `rootfs unpack` is now `snapshot unpack`
 - `apply` no longer exists. RIP"""
 
+  [notes.gc]
+  title= "Garbage collector improvements"
+  description = """\
+The garbage collector continues to improve with this release, including bug
+fixes on the client causing races and a new lease feature for making retention
+from the client easier.
+
+The lease API was added to make it easier for clients to prevent content and
+snapshots from being garbage collected while they are being actively worked on
+(such as from pull, import, or checkpoint). The API includes functions for
+creating, deleting, and listing leases. The lease gets attached to the context
+and the backend metadata store sees it and associates newly created content
+and snapshots with that lease.
+
+Leases are currently acquired and released automatically through the client.
+From the user perspective, fewer `gc.root` labels should be seen on client
+during pull/import operations or left over after a failed operation."""
+
 
 
 [breaking]