bin/nanoc in nanoc-4.0.0b4 vs bin/nanoc in nanoc-4.0.0rc1

@@ -1,5 +1,9 @@
 #!/usr/bin/env ruby
 require 'nanoc'
 require 'nanoc/cli'
 
+if File.file?('Gemfile') && !defined?(Bundler)
+  warn 'A Gemfile was detected, but Bundler is not loaded. This is probably not what you want. To run nanoc with Bundler, use `bundle exec nanoc`.'
+end
+
 Nanoc::CLI.run(ARGV)