[golang-syslog] Add documentation.

US-426 #progress

Change-Id: I30294414a62bd0633320832f9bca1be2cddbed07

development/languages/go/syslog.md

+# Syslog
+
+This document explains how to use golang syslogger library.
+
+
+## gn dependency
+
+```
+extra_dependencies = [
+    "//garnet/public/lib/syslog/go/src/syslog",
+    "//garnet/public/lib/app/go/src/app",
+]
+```
+
+### Initialization
+
+Logger can only be initialized once.
+
+#### Basic initialization
+
+```golang
+import (
+    "app/context"
+    "syslog/logger"
+)
+
+func main() {
+    ctx := context.CreateFromStartupInfo()
+    err := logger.InitDefaultLogger(ctx.GetConnector())
+}
+```
+
+#### Initialization with tags
+
+```golang
+import (
+    "app/context"
+    "syslog/logger"
+)
+
+func main() {
+    ctx := context.CreateFromStartupInfo()
+    // Global tags, max 4 tags can be passed. Every log message would be tagged using these.
+    err := logger.InitDefaultLoggerWithTags(ctx.GetConnector(), tag1, tag2)
+}
+```
+
+### Log messages
+
+```golang
+logger.Infof("my msg: %d", 10);
+
+// Allow message specific tagging. This message is going to be tagged with
+// this local tag and any global tag passed during initialization.
+logger.InfoTf("tag", "my msg: %d", 10);
+
+logger.Warnf("my msg: %d", 10);
+logger.WarnTf("tag", "my msg: %d", 10);
+
+logger.Errorf("my msg: %d", 10);
+logger.ErrorTf("tag", "my msg: %d", 10);
+
+logger.Fatalf("my msg: %d", 10);
+logger.FatalTf("tag", "my msg: %d", 10);
+
+logger.VLogf(1, "my msg: %d", 10); // verbose logs
+logger.VLogTf(1, "tag", "my msg: %d", 10); // verbose logs
+```
+
+### Reference
+[Golang APIs](https://fuchsia.googlesource.com/garnet/+/master/public/lib/syslog/go/src/syslog/logger/logger.go)