perf/scripts: Add perf-trace-python Documentation

Also small update to perf-trace-perl and perf-trace docs.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Keiichi KII <k-keiichi@bx.jp.nec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1264580883-15324-13-git-send-email-tzanussi@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>