Expand post-install message to clarify for new apps

Author: radar

i18n.gemspec

@@ -33,11 +33,15 @@ Gem::Specification.new do |s|
 HEADS UP! i18n 1.1 changed fallbacks to exclude default locale.
 But that may break your application.
 
+If you are upgrading your Rails application from an older version of Rails:
+
 Please check your Rails app for 'config.i18n.fallbacks = true'.
 If you're using I18n (>= 1.1.0) and Rails (< 5.2.2), this should be
 'config.i18n.fallbacks = [I18n.default_locale]'.
 If not, fallbacks will be broken in your app by I18n 1.1.x.
 
+If you are starting a NEW Rails application, you can ignore this notice.
+
 For more info see:
 https://github.com/svenfuchs/i18n/releases/tag/v1.1.0