add generating guides

data/registry/generate.go

@@ -21,6 +21,9 @@ type registry struct {
 	ProtocolID int `json:"protocol_id"`
 }
 
+// This file is generated with following command
+//  java -DbundlerMainClass="net.minecraft.data.Main" -jar server.jar --all
+// And you can found it at the generated\reports\ folder.
 //go:embed registries.json
 var registersJson []byte