perf tools: Update quipper information

This patch updates the links to the Quipper library.  It is now
available from GitHub and has been updated.

Reported-by: Lakshman Annadorai <lakshmana@google.com>
Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1520495985-2147-1-git-send-email-eranian@google.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>