Keep vm.rb and canonical instructions for it in this repo

README.md

@@ -67,6 +67,12 @@ There are a few extra scripts in the VM that you can use during the workshop:
 * `showargs` can be used to explain how command-line arguments work.
 * `vagrant` prints a message explaining that you're in the VM and should exit if you want to run a Vagrant command.
 
+## Additional Files
+
+Some files are not installed in the VM:
+
+* `vm.rb`: this is a Rails application template that students can apply to their app so that they don't have to pass `-b 0.0.0.0` to `rails server`. Copy it to the downloads site alongside the VM images, and have students apply it with `rake rails:template LOCATION=http://downloads.railsbridge.org/vm.rb`.
+
 ## Tests
 
 TODO: There should be some kind of automated test for the output (i.e. can you start the VM, log in, clone a test Rails app, and run it).

vm.rb

@@ -0,0 +1,22 @@
+# RailsBridge VM application template for running inside VirtualBox
+#
+# The VirtualBox NAT interface (which connects the guest to the host) is
+# probably 10.0.2.15, but just in case something changes in the future,
+# listen on all interfaces, and whitelist all 10.* networks.
+
+environment "config.web_console.whitelisted_ips = '10.0.0.0/8'", env: 'development'
+
+append_file 'config/boot.rb', <<EOF
+
+# Configure server for VirtualBox (added by RailsBridge VM)
+
+require 'rails/commands/server'
+
+module Rails
+  class Server
+    def default_options
+      super.merge(Host: '*', Port: 3000)
+    end
+  end
+end
+EOF