docs: Update usage of stream commands (#178)

Author: uki00a

README.md

@@ -50,8 +50,8 @@ const [stream] = await client.xread(
 );
 
 const msgFV = stream.messages[0].field_values;
-const plz = msgFV.get["yes"];
-const thx = msgFV.get["no"];
+const plz = msgFV["yes"];
+const thx = msgFV["no"];
 ```
 
 **Cluster**