readme: be explicit about what format refers to
## Quickstart
Root privilege is required to interact with the BPF virtual machine.
-The format is: `ConnID ReqID HeaderName HeaderValue`, except the first line that represents the HTTP protocol version.
+The log line format is: `ConnID ReqID HeaderName HeaderValue`, except the first line that represents the HTTP protocol version.
```
$ sudo h2olog -p $(pgrep -o h2o)
