logging: add comment to heroku create

Signed-off-by: Colton McCurdy <cmccurdy@fastly.com>

pkg/logging/heroku/create.go

@@ -22,6 +22,11 @@ type CreateCommand struct {
 func NewCreateCommand(parent common.Registerer, globals *config.Data) *CreateCommand {
 	var c CreateCommand
 
+	// Without this, parsing flags leads to panics.
+	// This is because if we try to scan directly into c.Input.<Field> without first
+	// creating a valid reference, flags will attempt to be scanned into null pointers.
+	// This will result in sending the zero value values for unset flags which is acceptable
+	// for Creates, but not Updates.
 	c.Input = fastly.CreateHerokuInput{
 		Name:              fastly.String(""),
 		Format:            fastly.String(""),