cmd/trace: document the final step to use pprof-like profiles
The tutorial ends without mentioning how to use the generated
pprof-like profile with the pprof tool. This may be very trivial
for users who are already very familiar with the Go tools, but
for the newcomers, it saves a lot of time to finalize the tutorial
with an example of `go tool pprof` invocation.
Change-Id: Idf034eb4bfb9672ef10190e66fcbf873e8f08f6a
Reviewed-on: https://go-review.googlesource.com/36803 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>