upd doc

Author: Snawoot

README.md

@@ -429,6 +429,8 @@ Usage of /home/user/go/bin/dumbproxy:
     	per-user bandwidth limit in bytes per second
   -bw-limit-buckets uint
     	number of buckets of bandwidth limit (default 1048576)
+  -bw-limit-burst int
+    	allowed burst size for bandwidth limit, how many "tokens" can fit into leaky bucket
   -bw-limit-separate
     	separate upload and download bandwidth limits
   -cafile string