Improve the demo experience

rails-app/bin/spring

@@ -0,0 +1,17 @@
+#!/usr/bin/env ruby
+
+# This file loads spring without using Bundler, in order to be fast.
+# It gets overwritten when you run the `spring binstub` command.
+
+unless defined?(Spring)
+  require 'rubygems'
+  require 'bundler'
+
+  lockfile = Bundler::LockfileParser.new(Bundler.default_lockfile.read)
+  spring = lockfile.specs.detect { |spec| spec.name == "spring" }
+  if spring
+    Gem.use_paths Gem.dir, Bundler.bundle_path.to_s, *Gem.path
+    gem 'spring', spring.version
+    require 'spring/binstub'
+  end
+end