log/syslog: document that Dial uses net.Dial parameters, add example

Fixes #16761

Change-Id: I709daa87926a31e5f8fd46a4c5ef69718ae349b1
Reviewed-on: https://go-review.googlesource.com/27209Reviewed-by: Chris Broadfoot <cbro@golang.org>

src/log/syslog/example_test.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !windows,!nacl,!plan9
+
+package syslog_test
+
+import (
+	"fmt"
+	"log"
+	"log/syslog"
+)
+
+func ExampleDial() {
+	sysLog, err := syslog.Dial("tcp", "localhost:1234",
+		syslog.LOG_WARNING|syslog.LOG_DAEMON, "demotag")
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Fprintf(sysLog, "This is a daemon warning with demotag.")
+	sysLog.Emerg("And this is a daemon emergency with demotag.")
+}

src/log/syslog/syslog.go

@@ -112,6 +112,8 @@ func New(priority Priority, tag string) (*Writer, error) {
 // writer sends a log message with the given facility, severity and
 // tag.
 // If network is empty, Dial will connect to the local syslog server.
+// Otherwise, see the documentation for net.Dial for valid values
+// of network and raddr.
 func Dial(network, raddr string, priority Priority, tag string) (*Writer, error) {
 	if priority < 0 || priority > LOG_LOCAL7|LOG_DEBUG {
 		return nil, errors.New("log/syslog: invalid priority")