[DOCS] Adds more validation details for data frame transforms (elastic#44714)

Author: lcawl

docs/reference/data-frames/apis/put-transform.asciidoc

@@ -31,6 +31,11 @@ information, see {stack-ov}/security-privileges.html[Security privileges] and
 [[put-data-frame-transform-desc]]
 ==== {api-description-title}
 
+When the {dataframe-transform} is created, a series of validations occur to
+ensure its success. For example, there is a check for the existence of the
+source indices and a check that the destination index is not part of the source
+index pattern.
+
 IMPORTANT:  You must use {kib} or this API to create a {dataframe-transform}.
             Do not put a {dataframe-transform} directly into any
             `.data-frame-internal*` indices using the Elasticsearch index API.

docs/reference/data-frames/apis/start-transform.asciidoc

@@ -27,6 +27,15 @@ have `view_index_metadata` privileges on the source index for the
 {stack-ov}/security-privileges.html[Security privileges] and
 {stack-ov}/built-in-roles.html[Built-in roles].
 
+[[start-data-frame-transform-desc]]
+==== {api-description-title}
+
+When a {dataframe-transform} starts, a series of validations occur to ensure its
+success. However, there are no initial privilege checks. If the user who created
+the transform does not have the required privileges on the source and
+destination indices, the transform starts but then fails when it attempts the
+unauthorized operation.
+
 [[start-data-frame-transform-path-parms]]
 ==== {api-path-parms-title}