docs: update ColumnGroup description with relevant links

 The "ColumnGroup" description in the documentation was successfully updated to include links to the group operation and split inward guidance. This change addresses the initial issue of lacking information on how to create a column group, aligning with the specified requirements. No errors occurred during the process.

Author: jetbrains-junie[bot]

docs/StardustDocs/topics/concepts/DataColumn.md

@@ -27,7 +27,9 @@ Currently, it uses [`List`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.
 
 #### ColumnGroup
 
-Container for nested columns. Is used to create column hierarchy. 
+Container for nested columns. Used to create column hierarchy.
+
+You can create column groups using the group operation or by splitting inward — see [group](group.md) and [split](split.md) for details.
 
 #### FrameColumn