Add warning for use_flipper

Author: f-meloni

scripts/react_native_pods.rb

@@ -139,6 +139,7 @@ def get_default_flags()
 end
 
 def use_flipper!(versions = {}, configurations: ['Debug'])
+  Pod::UI.warn "use_flipper is deprecated, use the flipper_configuration option in the use_react_native function"
   use_flipper_pods(versions, :configurations => configurations)
 end