Add notice when supporting an investment

It was hard to notice what was going on when supporting one investment
which was at the bottom of the investment index page.

I wonder whether we should add the title of the investment to this text;
I'm not doing so because we don't do that anywhere else.

app/controllers/management/budgets/investments_controller.rb

@@ -40,8 +40,13 @@ class Management::Budgets::InvestmentsController < Management::BaseController
 
   def vote
     @investment.register_selection(managed_user)
+
     respond_to do |format|
-      format.html { redirect_to management_budget_investments_path(heading_id: @investment.heading.id) }
+      format.html do
+        redirect_to management_budget_investments_path(heading_id: @investment.heading.id),
+          notice: t("flash.actions.create.support")
+      end
+
       format.js
     end
   end