feat: update readme

src/common/pprof/README.md

@@ -7,11 +7,16 @@ cargo build --features=pprof
 ```
 
 ## HTTP API
-Sample at 99 Hertz, for 5 seconds, output report in protobuf format.
+Sample at 99 Hertz, for 5 seconds, output report in [protobuf format](https://github.com/google/pprof/blob/master/proto/profile.proto).
 ```bash
 curl -s '0:4000/v1/prof/cpu' > /tmp/pprof.out
 ```
 
+Then you can use `pprof` command with the protobuf file.
+```bash
+go tool pprof -top /tmp/pprof.out
+```
+
 Sample at 99 Hertz, for 60 seconds, output report in flamegraph format.
 ```bash
 curl -s '0:4000/v1/prof/cpu?seconds=60&output=flamegraph' > /tmp/pprof.svg