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The existing link is outdated.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 <[email protected]>
Acked-by: Andi Kleen <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Chong Jiang <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>