Tweak documentation

Author: alextwoods

services/s3/src/main/java/software/amazon/awssdk/services/s3/multipart/ParallelConfiguration.java

@@ -41,7 +41,8 @@ public static Builder builder() {
     /**
      * The maximum number of concurrent part requests that are allowed for multipart operations, including both multipart
      * download (GetObject) and multipart upload (PutObject). This limits the number of parts that can be in flight at any
-     * given time, preventing the client from overwhelming the HTTP connection pool when transferring large objects.
+     * given time, preventing the client from overwhelming the HTTP connection pool when transferring large objects.  For
+     * getObject it applies only when the {@link AsyncResponseTransformer} supports parallel split.
      * Defaults to 50.
      *
      * @return The value for the maximum number of concurrent part requests.