Add documentation for Relay performance logger

Reviewed By: evanyeung Differential Revision: D67663334 fbshipit-source-id: 6203aec6e7f3ed29e8602d97c599af4749d67d98

Author: tyao1

website/sidebars.js

@@ -238,6 +238,7 @@ module.exports = {
  'debugging/fb/debugging-and-troubleshooting',
  'debugging/relay-devtools',
  'debugging/fb/network-logger',
+ 'debugging/fb/performance-logger',
  'debugging/inconsistent-typename-error',
  'debugging/declarative-mutation-directives',
  'debugging/fb/debugging-suspense',