Add guide to create a proposal or investment

During a Participatory Budget, some users are getting confused and
creating a proposal instead of a budget investment. This intermediate
page should help them create investments

Adding a feature flag just in case other forks don’t need this feature
and setting seeds and dev_seeds for appropriate initial setup

config/routes.rb

@@ -18,6 +18,7 @@ Rails.application.routes.draw do
   draw :direct_upload
   draw :document
   draw :graphql
+  draw :guide
   draw :legislation
   draw :management
   draw :moderation