Add post-install message to inform about the rename

See #28

Author: rosa

action_native_push.gemspec

@@ -20,6 +20,12 @@ Gem::Specification.new do |spec|
     Dir["{app,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
   end
 
+  spec.post_install_message = <<-MESSAGE
+    The "action_native_push" gem has been renamed to "action_push_native".
+    See: https://rubygems.org/gems/action_push_native
+    And: https://github.com/rails/action_push_native
+  MESSAGE
+
   spec.required_ruby_version = '>= 3.2.0'
 
   rails_version = ">= 8.0"