Creating a sample rails app to show deploying a GitHub-hosted app to Heroku. This turned out to be really easy (the key being git push heroku master, same as any Heroku app), so this is all overkill. But it's done now, so here we go.
(Misteps omitted)
Create repository in GitHub, pull down
git clone https://github.com/vgmcglaughlin/heroku-rails.git
cd heroku-rails/
Create rails app, add "welcome" controller Add app/views/welcome/index.html.erb and update config/routes.rb (not shown, see source)
rails new .
rails generate controller welcome
Run locally, check at http://localhost:3000
rails server
In Gemfile, replace gem 'sqlite3' with gem 'pg' (could have avoiding this by using the --database=postgresql option when creating the app), install bundle
bundle install
Log into Heroku, create new app
heroku login
heroku create
Check that remote "heroku" was added
git config -e
Commit everything
git add .
git commit -m "initial commit"
Push to GitHub
git push origin master
Push to Heroku
git push heroku master
Open Heroku deployed app (mine is at http://fast-temple-9343.herokuapp.com/)
heroku open