Improve documentation for postgres_auth_* configuration directives

config/environments/development.js.example

@@ -10,7 +10,10 @@ var config = {
     ,enable_cors: true
     ,cache_enabled: false
     ,log_format: '[:date] :req[X-Real-IP] :method :req[Host]:url :status :response-time ms -> :res[Content-Type] (:res[X-Tiler-Profiler])'
+    // Templated database username for authorized user
+    // Supported labels: 'user_id' (read from redis)
     ,postgres_auth_user: 'development_cartodb_user_<%= user_id %>'
+    // Templated database password for authorized user
     // Supported labels: 'user_id', 'user_password' (both read from redis)
     ,postgres_auth_pass: '<%= user_password %>'
     ,postgres: {