Add comment about runtime initializing class for google cloud SQL

Closes quarkusio/quarkus#36996

_guides/deploying-to-google-cloud.adoc

@@ -290,6 +290,15 @@ quarkus.vertx.prefer-native-transport=true
 
 WARNING: This only works when your application is running inside a Google Cloud managed runtime like App Engine.
 
+=== Using Cloud SQL with native executables
+
+When using native executables, you also need to mark `jnr.ffi.provider.jffi.NativeFinalizer$SingletonHolder` as runtime initialized.
+
+[source,bash]
+----
+quarkus.native.additional-build-args=--initialize-at-run-time=jnr.ffi.provider.jffi.NativeFinalizer$SingletonHolder
+----
+
 == Going further
 
 You can find a set of extensions to access various Google Cloud Services in the Quarkiverse (a GitHub organization for Quarkus extensions maintained by the community),