Update sql-machine-learning-services-windows-install.md

Adding clarification that the feature cannot be installed in an existing FCI and must be installed during installation time.

Author: joshts0

docs/machine-learning/install/sql-machine-learning-services-windows-install.md

@@ -21,11 +21,11 @@ This article shows you how to install [SQL Server Machine Learning Services](../
 
 ## <a name="bkmk_prereqs"> </a> Pre-installation checklist
 
-+ A database engine instance is required. You can't install just Python or R features, although you can add them incrementally to an existing instance.
++ A database engine instance is required. You can't install just Python or R features, although you can add them incrementally to an existing **standalone** instance.
 
 + For business continuity, [Always On availability groups](../../database-engine/availability-groups/windows/overview-of-always-on-availability-groups-sql-server.md) are supported for Machine Learning Services. Install Machine Learning Services, and configure packages, on each node.
 
-+ Installing Machine Learning Services *is not supported* on an [Always On failover cluster instance](../../sql-server/failover-clusters/windows/always-on-failover-cluster-instances-sql-server.md) in SQL Server 2017. It's supported with SQL Server 2019 and later.
++ Installing Machine Learning Services *is not supported* on an [Always On failover cluster instance](../../sql-server/failover-clusters/windows/always-on-failover-cluster-instances-sql-server.md) in SQL Server 2017. It's supported with SQL Server 2019 and later. You must install Machine Learning Services at installation time, and features cannot be added to an existing failover instance once installed.
 
 + Don't install Machine Learning Services on a domain controller. The Machine Learning Services portion of setup will fail.
 
@@ -392,4 +392,4 @@ Python developers can learn how to use Python with SQL Server by following these
 R developers can get started with some simple examples and learn the basics of how R works with SQL Server. For your next step, see the following links:
 
 + [Quickstart: Run R in T-SQL](../tutorials/quickstart-r-create-script.md)
-+ [Tutorial: In-database analytics for R developers](../tutorials/r-taxi-classification-introduction.md)
++ [Tutorial: In-database analytics for R developers](../tutorials/r-taxi-classification-introduction.md)