update readme.md

```go
viper.WatchConfig()
viper.OnConfigChange(func(e fsnotify.Event) {
	fmt.Println("Config file changed:", e.Name)
})
```
this code will cause data race,  please check this question:
https://stackoverflow.com/questions/68915944/viper-dynamically-loading-config-file-has-data-race/68919971#68919971

README.md

@@ -175,10 +175,10 @@ Optionally you can provide a function for Viper to run each time a change occurs
 **Make sure you add all of the configPaths prior to calling `WatchConfig()`**
 
 ```go
-viper.WatchConfig()
 viper.OnConfigChange(func(e fsnotify.Event) {
 	fmt.Println("Config file changed:", e.Name)
 })
+viper.WatchConfig()
 ```
 
 ### Reading Config from io.Reader