add link to @sigstore/bundle in root README (#612)

Signed-off-by: Brian DeHamer <bdehamer@github.com>

README.md

@@ -5,6 +5,7 @@ JavaScript libraries for interacting with [Sigstore][6] services.
 ## Packages
 
 * [`sigstore`](./packages/client) - Client library implementing Sigstore signing/verification workflows.
+* [`@sigstore/bundle`](./packages/bundle) - TypeScript types and utility functions for working with Sigstore bundles.
 * [`@sigstore/cli`](./packages/cli) - Command line interface for signing/verifying artifacts with Sigstore.
 * [`@sigstore/tuf`](./packages/tuf) - Library for interacting with the Sigstore TUF repository.
 * [`@sigstore/rekor-types`](./packages/rekor-types) - TypeScript types for the Sigstore Rekor REST API.