Update README.md

Author: Leeon123

README.md

@@ -22,8 +22,15 @@ Then:
 
     git clone https://github.com/Leeon123/golang-httpflood.git
 
+Header.txt format:
+
+    Accept: text/html
+    User-agent: Wget
+    Referer: http://google.com
+
+Or anything else of http header. If you don't have any idea of this please just use nil for using default random header.
 ## Usage
 
     cd golang-httpflood
     go build httpflood.go
-    ./httpflood 
+    ./httpflood  <ip> <port> <threads> <page> <get/post> <seconds> <header.txt/nil>