Update readme.md

Author: perrysk-msft

samples/manage/windows-containers/mssql-server-2014-express-windows/readme.md

@@ -34,10 +34,8 @@ To run this sample, you need the following prerequisites.
 <a name=run-this-sample></a>
 
 ## Run this sample
-Use the Dockerfile and execute the following two commands to build and run sqlexpress:
-
-1. docker build --env sa_password=<YOUR_SA_PASSWORD> <IMAGE NAME> .
-2. docker run -it -p 1433:1433 <IMAGE NAME>
+The image provides one environment variable to set the sa password: </br>
+- sa_password: Sets the sa password and enables the sa login
 
 <a name=sample-details></a>