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 <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20200311122034.3697-4-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/intel-pt.txt

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