readme - proxy-agent set StreamConn url

Author: Shlomi Kushchi

README.md

@@ -341,6 +341,7 @@ For that exact purpose this ![project](https://github.com/shlomikushchi/alpaca-p
 The steps to execute this are:
 * Run the Alpaca Proxy Agent as described in the project's README
 * Define this env variable: `DATA_PROXY_WS` to be the address of the proxy agent. (e.g: `DATA_PROXY_WS=ws://127.0.0.1:8765`)
+* If you are using the Alpaca data stream, make sure you you initiate the StreamConn object with the container's url, like so: data_url='http://127.0.0.1:8765'
 * execute your algorithm. it will connect to the servers through the proxy agent allowing you to execute multiple strategies