updated installation code samples to use Stimulus constant

[bgartenmann]

in v1.x the application constant was renamed to Stimulus, but this was not yet reflected in the README.

[tonysm]

Thanks! I'll merge it to reflect the current state, but I'm starting to regret that decision. The Rails folks use application for this (see here). I'm inclined to use that as well and rename the file to be controller/application.js as well. Do you have any thoughts on that @bgartenmann ?

[bgartenmann]

@tonysm What was the reason to change it from application to Stimulus for the 1.x version?
And what makes you regret it now? Any issues with it?
I guess having it the same way as in stimulus-rails is not wrong, however it's mostly a one time set it and forget it, no?

[tonysm]

I wasn't sure if I liked the name application, but now calling it Stimulus is kinda misleading because we have a global Stimulus lib, so the application is really the right name for the application instance (plus, it's the same language they use upstream, so it's a safer bet to avoid confusion, I guess)