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>

src/cmd/trace/main.go

@@ -2,28 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-/*
-Trace is a tool for viewing trace files.
-
-Trace files can be generated with:
-	- runtime/trace.Start
-	- net/http/pprof package
-	- go test -trace
-
-Example usage:
-Generate a trace file with 'go test':
-	go test -trace trace.out pkg
-View the trace in a web browser:
-	go tool trace trace.out
-Generate a pprof-like profile from the trace:
-	go tool trace -pprof=TYPE trace.out > TYPE.pprof
-
-Supported profile types are:
-	- net: network blocking profile
-	- sync: synchronization blocking profile
-	- syscall: syscall blocking profile
-	- sched: scheduler latency profile
-*/
 package main
 
 import (