add intro sentence

Author: kilfoyle

manage-data/lifecycle/data-stream.md

@@ -24,6 +24,8 @@ A data stream lifecycle also supports downsampling the data stream backing indic
 
 ## Availability
 
+Note the availability of data stream lifecycle to ensure that it's applicable for your use case:
+
 * Data stream lifecycle is supported only for data streams and cannot be used with standalone indices.
 
 * Like {{ilm-cap}} ({{ilm-init}}), data stream lifecycle is supported in both {{ecloud}} and self-managed environments. Data stream lifecycle is less feature rich than {{ilm-init}} and is focused on simplicity. For a detailed comparison refer to [Data lifecycle](/manage-data/lifecycle.md).

manage-data/lifecycle/index-lifecycle-management.md

@@ -23,6 +23,8 @@ products:
 
 ## Availability
 
+Note the availability of {{ilm-init}} to ensure that it's applicable for your use case:
+
 * {{ilm-init}} is supported for both data streams and standalone indices:
 
     * **Data stream:** A [data stream](/manage-data/data-store/data-streams.md) acts as a layer of abstraction over a set of indices that contain append-only, time series data. You can configure {{ilm-init}} using a data stream as a single named resource, so that rollover and any other configured actions are performed on the data stream's backing indices automatically.