Improve config handling

- Backup existing config if we're saving it to add configuration
  defaults
- Output messages when saving/backing up the configuration file

pkg/cli/config.go

@@ -44,9 +44,10 @@ func NewConfig() (*Config, error) {
 	shouldWriteDefaults := false
 	c := &Config{}
 
+	configExists := true
 	configBytes, err := os.ReadFile(configFile)
 	if os.IsNotExist(err) {
-		shouldWriteDefaults = true
+		configExists = false
 	} else if err != nil {
 		return nil, fmt.Errorf("Could not read config file: %v", err)
 	} else {
@@ -54,7 +55,12 @@ func NewConfig() (*Config, error) {
 	}
 
 	shouldWriteDefaults = SetStructDefaults(c)
-	if shouldWriteDefaults {
+	if !configExists || shouldWriteDefaults {
+		if configExists {
+			fmt.Printf("Saving new defaults to configuration, backing up existing configuration to %s\n", configFile + ".bak")
+			os.Rename(configFile, configFile + ".bak")
+		}
+		fmt.Printf("Writing configuration file to %s\n", configFile)
 		file, err := os.Create(configFile)
 		if err != nil {
 			return nil, fmt.Errorf("Could not open config file for writing: %v", err)