Add the documentation for :spacer_template in partial rendering

I just found out that in action_view/render/partials.rb there was an option called :spacer_template which you can specify in render :template => 'template_name', :collection => @collection call. It will render the spacer template and put it between each object partial.

I think the documentation for this option has been left out from Rails 2 -> Rails 3 migration, as I found test case exists in the test directory for this feature. Also, I found the documentation of this option in Rails 2.

So, I've upload a patch which will add some description on how to use that feature. Patch is attached to this ticket.

I don't know if this is appropriate place to put it or not, but if not then please let me know.

Thank you