Stub out Sled trees for zebra-client / blockchain scanning state
@@ -149,10 +149,21 @@ blocks to other peers, as they are validated.
## Online client component
-This component maintains its own sled tree. See RFC#0005
+This component maintains its own Sled tree. See RFC#0005 for more details on Sled.
-```
-```
+We use the following Sled trees:
+
+| Tree | Keys | Values |
+|-----------------------|-----------------------|-------------------------------------|
+| `viewing_keys` | `IncomingViewingKey` | `String` |
+| `height_by_key` | `IncomingViewingKey` | `BE32(height)` |
+| `received_set_by_key` | `IncomingViewingKey` | ? |
+| `spend_set_by_key` | `IncomingViewingKey` | ? |
+| `nullifier_map_by_key`| `IncomingViewingKey` | ? |
+
+See https://zips.z.cash/protocol/protocol.pdf#saplingscan
+
+Zcash structures are encoded using `ZcashSerialize`/`ZcashDeserialize`.
This component runs inside zebrad. After incoming viewing keys are registered,
it holds onto them in order to do blockchain scanning. The component keeps track
