Install Hotwire Spark by default

[louis-antonopoulos]

Hotwire Spark is very helpful in Development to provide automatic reloading of views when filesystem changes are detected.

Source: ReadySetGo Issue 40: Add Hotwire Spark to /rails and generated apps

[cpytel]

This is actually what we envisioned, so that the user can see the app to come together within an iframe.

[stevepolitodesign]

Addressed in #1342