googlecloudstorage: add example values for endpoint with help on avoiding transfer fees

backend/googlecloudstorage/googlecloudstorage.go

@@ -337,8 +337,9 @@ can't check the size and hash but the file contents will be decompressed.
 			Default:  false,
 		}, {
 			Name:     "endpoint",
-			Help:     "Endpoint for the service.\n\nLeave blank normally.",
+			Help:     "Endpoint for the service. Use a regional endpoint (storage.REGION.rep.googleapis.com) to reduce transfer fees",
 			Advanced: true,
+			Examples: getHelpForEndpoints(),
 		}, {
 			Name:     config.ConfigEncoding,
 			Help:     config.ConfigEncodingHelp,

backend/googlecloudstorage/googlecloudstorageendpoints.go

@@ -0,0 +1,35 @@
+package googlecloudstorage
+
+import (
+	"fmt"
+
+	"github.com/rclone/rclone/fs"
+)
+
+type endpointRecord struct {
+	endpointURL, Location, Description string
+}
+
+var endpoints = []endpointRecord{
+	{"https://storage.europe-west3.rep.googleapis.com/storage/v1/", "europe-west3", "Frankfurt"},
+	{"https://storage.europe-west8.rep.googleapis.com/storage/v1/", "europe-west8", "Milan"},
+	{"https://storage.europe-west9.rep.googleapis.com/storage/v1/", "europe-west9", "Paris"},
+	{"https://storage.me-central2.rep.googleapis.com/storage/v1/", "me-central2", "Doha"},
+	{"https://storage.us-central1.rep.googleapis.com/storage/v1/", "us-central1", "Iowa"},
+	{"https://storage.us-east1.rep.googleapis.com/storage/v1/", "us-east1", "South Carolina"},
+	{"https://storage.us-east4.rep.googleapis.com/storage/v1/", "us-east4", "Northern Virgina"},
+	{"https://storage.us-east5.rep.googleapis.com/storage/v1/", "us-east5", "Columbus"},
+	{"https://storage.us-south1.rep.googleapis.com/storage/v1/", "us-south1", "Dallas"},
+	{"https://storage.us-west1.rep.googleapis.com/storage/v1/", "us-west1", "Oregon"},
+	{"https://storage.us-west2.rep.googleapis.com/storage/v1/", "us-west2", "Los Angeles"},
+	{"https://storage.us-west3.rep.googleapis.com/storage/v1/", "us-west3", "Salt Lake City"},
+	{"https://storage.us-west4.rep.googleapis.com/storage/v1/", "us-west4", "Las Vegas"},
+}
+
+func getHelpForEndpoints() (r []fs.OptionExample) {
+	r = make([]fs.OptionExample, 0, len(endpoints))
+	for _, ep := range endpoints {
+		r = append(r, fs.OptionExample{Value: ep.endpointURL, Help: fmt.Sprintf("%s : %s", ep.Location, ep.Description)})
+	}
+	return r
+}