doc: ngx.req.socket should be put near its description (#276)

Author: spacewander

README.md

@@ -319,9 +319,10 @@ other stream modules.
     `ngx.ERR`, `ngx.WARN`, and etc.
 * [print](https://github.com/openresty/lua-nginx-module#print)
 * [ngx.ctx](https://github.com/openresty/lua-nginx-module#ngxctx)
-* [ngx.req.socket](https://github.com/openresty/lua-nginx-module#ngxreqsocket)
 * [ngx.balancer](https://github.com/openresty/lua-resty-core/blob/master/lib/ngx/balancer.md)
 
+* [ngx.req.socket](https://github.com/openresty/lua-nginx-module#ngxreqsocket)
+
 Only raw request sockets are supported, for obvious reasons. The `raw` argument value
 is ignored and the raw request socket is always returned. Unlike ngx_http_lua,
 you can still call output API functions like `ngx.say`, `ngx.print`, and `ngx.flush`