update readme

@@ -325,14 +325,12 @@ vhost hooks.callback.srs.com {
         # when dvr got flv header, call the hook,
         # the request in the POST data string is a object encode by json:
         #       {
-        #           "action": "on_dvr_reap_flv",
+        #           "action": "on_dvr_reap_flv_header",
         #           "vhost": "video.test.com", "app": "live",
         #           "stream": "livestream",
         #           "segment": {
         #               "cwd": "/usr/local/srs",
-        #               "path": "./objs/nginx/html/live/livestream.1398315892865.flv",
-        #               "duration": 1001, "offset":0,
-        #               "has_keyframe": true, "pts":1398315895958
+        #               "path": "./objs/nginx/html/live/livestream.header.flv"
         #           }
         #       }
         # when dvr reap flv file, call the hook,