Include a javascript runtime when generate the app

Hello, I'm opening this thread in order to discuss a frustration that
I have since Rails 3.1

I am teacher in private courses and university in Brazil and my main
language is Ruby (along with Rails for web classes). I have more than
a thousand students and I'm starting to know very well which part of
Rails and Ruby are hard to explain for beginners.

A lot of people said that Rails is getting less friendly for beginners
but that's not true and I can assure that it's not true in most of the
points except for one:

"Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs
for a list of available runtimes. (ExecJS::RuntimeUnavailable)"

In last two or three month I trainned more than a hundred new students
and answered at least 10 times why they need to install a Javascript
Runtime for a tool that's based in Ruby. Most of people don't even now
that you can run Javascript outside the browsers, and if you can, what
are the benefits.

I really advocate first class front-development and I love the
additions of Rails 3.1 but we need to make it easier to start.

Not everybody is using OSX and require people to install nodejs or
manually open the Gemfile to add therubyracer it's not a good solution
(specially when I present Rails as webdevelopment without pain).

So, I would like to raise the discussion about this issue:

https://github.com/rails/rails/pull/3619#issuecomment-2773673

Maybe the Gemfile is not the right place for the checking. Probably we
could move it to ExecJS?