perf archive: Explain how to use the generated tarball

[root@doppio ~]# perf archive
 Now please run:

 $ tar xvf perf.data.tar.bz2 -C ~/.debug

 wherever you need to run 'perf report' on.
 [root@doppio ~]#

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1269365638-10223-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>