This might be obvious but it still took me some Makefile reading. Add it
to README to make it easier for others.

Link: https://lore.kernel.org/linux-trace-devel/20220815031342.775201-2-joel@joelfernandes.org



Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>