Set up RSpec test framework

- Add rspec-rails to the development/test group
- Generate RSpec config (.rspec, spec_helper, rails_helper)
- Add home page request spec as a smoke test
- Stop ignoring .rspec so test config is tracked

Gemfile

@@ -54,6 +54,9 @@ group :development, :test do
 
   # Omakase Ruby styling [https://github.com/rails/rubocop-rails-omakase/]
   gem "rubocop-rails-omakase", require: false
+
+  # RSpec testing framework for Rails [https://github.com/rspec/rspec-rails]
+  gem "rspec-rails"
 end
 
 group :development do