docs: product ID 1599715149861306368 is the "RCF 3" mop (#5)

On my RCF 3 at least, this is what gets stored into `Device.product_id`.
Also, there's no "RCF 5" among the vendor's released products.

Fixes: 7b02c06

Author: jktjkt

PROTOCOL.md

@@ -18,7 +18,7 @@ zone = "GBR"
 
 * RCV3 - `1528986273083777024`
 * RCV5 - `1540149850806333440`
-* RCF5 - `1599715149861306368`
+* RCF3 - `1599715149861306368`
 
 ## Work mode