lib/model: Log folder IDs and labels (fixes #3724)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3741

lib/config/folderconfiguration.go

@@ -7,6 +7,7 @@
 package config
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -103,6 +104,10 @@ func (f *FolderConfiguration) HasMarker() bool {
 	return true
 }
 
+func (f FolderConfiguration) Description() string {
+	return fmt.Sprintf("%q (%s)", f.Label, f.ID)
+}
+
 func (f *FolderConfiguration) DeviceIDs() []protocol.DeviceID {
 	deviceIDs := make([]protocol.DeviceID, len(f.Devices))
 	for i, n := range f.Devices {