add: 添加Brief (#482)

* add brief

* fix: README中插件位置

plugin/image_finder/keyword.go

@@ -64,8 +64,8 @@ var hrefre = regexp.MustCompile(`<a href=".*">`)
 func init() {
 	control.Register("imgfinder", &ctrl.Options[*zero.Ctx]{
 		DisableOnDefault: false,
-		Help: "关键字搜图\n" +
-			"- 来张 [xxx]",
+		Brief:            "关键字搜图",
+		Help:             "- 来张 [xxx]",
 	}).OnRegex(`^来张\s?(.*)$`, zero.AdminPermission).SetBlock(true).
 		Handle(func(ctx *zero.Ctx) {
 			keyword := ctx.State["regex_matched"].([]string)[1]