conf(): updated sample config and root_url to better explain it

conf/sample.ini

@@ -42,8 +42,9 @@
 # Prevents DNS rebinding attacks
 ;enforce_domain = false
 
-# The full public facing url
-;root_url = %(protocol)s://%(domain)s:%(http_port)s/
+# The full public facing url you use in browser, used for redirects and emails
+# If you use reverse proxy and sub path specify full url (with sub path)
+;root_url = http://localhost:3000
 
 # Log web requests
 ;router_logging = false