Write up a case study around Facebook Container

https://profiler.firefox.com/public/988942be9f2bd9fb499435792f93e0ce4ca5f657/flame-graph/?globalTrackOrder=7-8-0-1-2-3-4-5-6&hiddenGlobalTracks=7-8-0-1-2-3-4-6&hiddenLocalTracksByPid=26481-0&localTrackOrderByPid=26458-1-0~26800-0~26481-0~26707-0~&range=0.5739_5.3985&search=message&thread=6&v=4

I got feedback that just explaining how the tools work isn't useful, we should include some more tutorial-focused case studies.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-240)