simplify usage

@@ -33,7 +33,7 @@ git clone https://github.com/winlinvip/simple-rtmp-server &&
 cd simple-rtmp-server/trunk
 </pre>
 <strong>Step 2:</strong> build SRS,
-<strong>Requires: Centos6.x 64bits, others see [Build](https://github.com/winlinvip/simple-rtmp-server/wiki/Build)</strong><br/>
+<strong>Requires Centos6.x 64bits, others see [Build](https://github.com/winlinvip/simple-rtmp-server/wiki/Build)</strong><br/>
 <pre>
 ./configure --with-ssl --without-hls --without-ffmpeg --without-http && make
 </pre>