Update documentation

storage/config.go

@@ -2,6 +2,7 @@ package storage
 
 // Config is the configuration for alerting providers
 type Config struct {
-	// File is the path of the file to use when using file.Store
+	// File is the path of the file to use for persistence
+	// If blank, persistence is disabled.
 	File string `yaml:"file"`
 }