perf intel-pt: Update intel-pt.txt file with new location of the documentation

Make it easy for people looking in intel-pt.txt to find the new file.

Signed-off-by: Adrian Hunter <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/intel-pt.txt

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+Documentation for support for Intel Processor Trace within perf tools' has moved to file perf-intel-pt.txt