do performance test, support 2.7kclient, 500kbps

@@ -366,10 +366,10 @@ Supported operating systems and hardware:
 
 ## Performance
 
-Performance benchmark history:
-* 2014-07-12, [SRS 0.9.156, virtual box, 2700clients, 89%CPU, 61MB](https://github.com/winlinvip/simple-rtmp-server/commit/6d12280b7cc54c465b1caf8b1402149e77c4c7d9)
-* 2014-07-12, [SRS 0.9.156, virtual box, 1800clients, 68%CPU, 38MB](https://github.com/winlinvip/simple-rtmp-server/commit/e2d273f4939348374bf9644df9d54c4293b39c1a)
-* 2013-11-28, [SRS 0.5.0, virtual box, 1800clients, 90%CPU, 41MB](https://github.com/winlinvip/simple-rtmp-server/commit/023e23bc8261bec15a70a7ae932098fb4f82b679)
+Performance benchmark history, on virtual box:
+* 2014-07-12, SRS 0.9.156, 2700clients, 89%CPU, 61MB. [benchmark](https://github.com/winlinvip/simple-rtmp-server/commit/6d12280b7cc54c465b1caf8b1402149e77c4c7d9)
+* 2014-07-12, SRS 0.9.156, 1800clients, 68%CPU, 38MB. [benchmark](https://github.com/winlinvip/simple-rtmp-server/commit/e2d273f4939348374bf9644df9d54c4293b39c1a)
+* 2013-11-28, SRS 0.5.0, 1800clients, 90%CPU, 41MB. [benchmark](https://github.com/winlinvip/simple-rtmp-server/commit/023e23bc8261bec15a70a7ae932098fb4f82b679)
 
 1.  300 connections,  150Mbps, 500kbps, CPU 5.7%, MEM 9208KB.
 1.  600 connections,  300Mbps, 500kbps, CPU 18.3%, MEM 13MB.