Fixed extentions readme file (#2603)

Co-authored-by: Gerald Venzl <[email protected]>

Author: aditya059

OracleDatabase/SingleInstance/extensions/README.md

@@ -1,6 +1,6 @@
 # Build Extensions
 
-After creating the base image using buildDockerImage.sh, use buildExtensions.sh to build an extended image that will include all features present under the extensions folder.
+After creating the base image using buildContainerImage.sh, use buildExtensions.sh to build an extended image that will include all features present under the extensions folder.
 
 Once you have created the base image, go into the **extensions** folder and run the **buildExtensions.sh** script:
 
@@ -21,4 +21,4 @@ LICENSE UPL 1.0
 
 Copyright (c) 2020 Oracle and/or its affiliates. All rights reserved.
 
-The resulting image can be used in the same fashion as the base image.
+The resulting image can be used in the same fashion as the base image.