add example for session handling of ghttp

.example/net/ghttp/server/session/session_map.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/gogf/gf/frame/g"
+	"github.com/gogf/gf/net/ghttp"
+)
+
+func main() {
+	s := g.Server()
+	s.SetSessionMaxAge(60)
+	s.BindHandler("/set", func(r *ghttp.Request) {
+		r.Session.Set("captcha", map[string]string{
+			"key": "value",
+		})
+		r.Response.Write("ok")
+	})
+	s.BindHandler("/get", func(r *ghttp.Request) {
+		fmt.Println(r.Session.Get("captcha"))
+		r.Response.Write(r.Session.Get("captcha"))
+	})
+	s.SetPort(8199)
+	s.Run()
+}