perf tool: add example to perf-trace documentation

While at it, update the synopsis to include options.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: David Ahern <dsahern@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf tool: ignore output from timechart

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf tool: add example to perf-timechart documentation

While at it, update the synopsis to show both forms.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
perf tool: report user-friendly error from timechart

Earlier, when 'timechart record' was invoked by a user without
permissions to debugfs:

$ perf timechart record
invalid or unsupported event: 'power:cpu_frequency'
Run 'perf list' for a list of valid events

 usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]
[... detailed usage information ...]

This is highly user unfriendly, as the real problem is not reported to
the user correctly. Now, the user gets a much more friendly:

$ perf timechart record
Error:  No permissions to read $debugfs/tracing/events/power/cpu_frequency
Hint:   Change the permissions of debugfs: /sys/kernel/debug
        The directory will be present if your kernel was compiled with debugfs support.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf tool: report user-friendly errors from trace

Currently, execution of 'perf trace' reports the following cryptic
message to the user:

$ perf trace
Couldn't read the raw_syscalls tracepoints information!

Typically this happens because the user does not have permissions to
read the debugfs filesystem. Also handle the case when the kernel was
not compiled with debugfs support or when it isn't mounted.

Now, the tool prints detailed error messages:

$ perf trace
Error:  Unable to find debugfs
Hint:   Was your kernel was compiled with debugfs support?
Hint:   Is the debugfs filesystem mounted?

$ perf trace
Error:  No permissions to read $debugfs/tracing/events/raw_syscalls
Hint:   Change the permissions of the debugfs filesystem

Cc: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>