perf docs: Improve help information in perf.txt

perf has many undocumented options, such as:-vv, --exec-path,
--html-path, -p, --paginate,--no-pager, --debugfs-dir, --buildid-dir,
--list-cmds, --list-opts.

Add entris for these options in perf.txt.

Signed-off-by: Zejiang Tang <tangzejiang@loongson.cn>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Link: http://lore.kernel.org/lkml/1599645194-8438-1-git-send-email-tangzejiang@loongson.cn


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>