Rough-draft upgrade settings documentation [#8]

internal/helm/plan.go

@@ -67,6 +67,7 @@ func determineSteps(cfg Config) *func(Config) []Step {
 		return &help
 	default:
 		switch cfg.DroneEvent {
+		// Note: These events are documented in docs/upgrade_settings.yml. Any changes here should be reflected there.
 		case "push", "tag", "deployment", "pull_request", "promote", "rollback":
 			return &upgrade
 		case "delete":

internal/run/upgrade.go

@@ -25,6 +25,8 @@ func (u *Upgrade) Execute(_ Config) error {
 }
 
 // Prepare gets the Upgrade ready to execute.
+// Note: mandatory settings are documented in README.md, and the full list of settings is in docs/upgrade_settings.yml.
+// Any additions or deletions here should be reflected there.
 func (u *Upgrade) Prepare(cfg Config) error {
 	if u.Chart == "" {
 		return fmt.Errorf("chart is required")