+ add usage

Author: kebe7jun

README.md

@@ -1,2 +1,52 @@
 # process-monitor
 process-monitor is a Go language library for observing the life cycle of system processes.
+
+## Usage
+
+```go
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/signal"
+	"syscall"
+
+	processwatcher "github.com/merbridge/process-watcher"
+)
+
+func main() {
+	w := processwatcher.NewProcessWatcher()
+	if err := w.Start(); err != nil {
+		panic(err)
+	}
+	sigs := make(chan os.Signal, 1)
+	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
+	for {
+		select {
+		case e := <-w.Events():
+			if e.Err != nil {
+				panic(e.Err)
+			}
+			typ := "not-support"
+			var obj interface{}
+			switch e.GetType() {
+			case processwatcher.PROC_EVENT_EXEC:
+				typ = "exec"
+				obj = e.GetExec()
+			case processwatcher.PROC_EVENT_FORK:
+				typ = "fork"
+				obj = e.GetFork()
+			case processwatcher.PROC_EVENT_EXIT:
+				typ = "exit"
+				obj = e.GetExit()
+			}
+			fmt.Printf("%s: %+v\n", typ, obj)
+		case <-sigs:
+			return
+		}
+	}
+}
+```
+
+> Nit: Requires a root user to run, you can run as: `go run -exec sudo ./app`