perf tools: Update documentation info about quipper

perf tools: Update documentation info about quipper

The existing link is outdated. The most recent quipper code can be found at the
new URL.

Committer notes:

Quipper is a C++ parser that can be used to convert from a perf.data
file to and from a protobuf, a Chromium OS facility.

Signed-off-by: Simon Que <sque@chromium.org>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Chong Jiang <chongjiang@chromium.org>
Link: http://lkml.kernel.org/n/tip-4q1nm7jl3vovp66p5bki20pq@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>