tutorial: Bug hunting: Find the sleep in app

[tahini]

We could provide our own version of some common app, like ls or grep, where we added a few sleeps or time-consuming do-nothing routine.

We would show how to compile the application with the -finstrument-functions flag and obtain an lttng trace with func_entry/func_exits, and also get kernel trace. The goal would be the find where the sleeps are in the app, using critical path and callstack views.