docs: Gator syncset doc (#2833)

Signed-off-by: Anlan Du <adu47249@gmail.com>
Co-authored-by: alex <8968914+acpana@users.noreply.github.com>
Co-authored-by: Rita Zhang <rita.z.zhang@gmail.com>

docs/design/README.md

@@ -11,6 +11,7 @@ Generally, design docs are on Google docs:
 * [Sync Resource](https://docs.google.com/document/d/1ZbXaEh7v_HcgrRu7N-kEucU2pXyq1Rt7cSmmFOBN2q8/edit)
 * [External Data Response Cache](https://docs.google.com/document/d/1nl6iWMmh9CRT0A6cr-Nkfofv9wp210Bkf6ilLq9LLBo/edit)
 * [Export violations using pub-sub](https://docs.google.com/document/d/14QVzdn_fncYLIfZUusCpzrFGWR_aBth_OsR1EsynQeA/edit?usp=sharing)
+* [Gator SyncSet Support](https://docs.google.com/document/d/1mBvy6Y7TDyZswdYlFBHB3Mi2irLVqga_7ZoZvfPIU0A/edit)
 
 ## Implemented
 * [Gatekeeper V3 Accepted Design](https://docs.google.com/document/d/1yC4wgpVoJj6ngYnSTtO-HeaIBl05gla562sD7qKPy3M/edit#heading=h.z0bjqzl81dpe)