Add themesDir to exampleSite config

So it is runnable out-of-the-box.

exampleSite/config.toml

 baseURL = "https://example.com"
 languageCode = "en-us"
 theme = "gohugo-theme-ananke"
+themesDir = "../.."
 
 MetaDataFormat = "yaml"
 DefaultContentLanguage = "en"