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

db/seeds.rb

@@ -85,6 +85,7 @@ Setting['feature.user.recommendations'] = true
 Setting['feature.community'] = true
 Setting['feature.map'] = nil
 Setting['feature.allow_images'] = true
+Setting['feature.guides'] = nil
 
 # Spending proposals feature flags
 Setting['feature.spending_proposal_features.voting_allowed'] = nil