more extension properties topic refs

Author: AndreiKingsley

docs/StardustDocs/topics/guides/Guides-And-Examples.md

@@ -24,6 +24,9 @@ Explore our structured, in-depth guides to steadily improve your Kotlin DataFram
 
 <img src="quickstart_preview.png" border-effect="rounded" width="705"/>
 
+* [](extensionPropertiesApi.md) — learn about extension properties for `DataFrame` 
+and make working with your data both convenient and type-safe.
+
 * [Enhanced Column Selection DSL](https://blog.jetbrains.com/kotlin/2024/07/enhanced-column-selection-dsl-in-kotlin-dataframe/)
   — explore powerful DSL for typesafe and flexible column selection in Kotlin DataFrame.
 * [](Kotlin-DataFrame-Features-in-Kotlin-Notebook.md)

docs/StardustDocs/topics/guides/quickstart.md

@@ -351,6 +351,9 @@ Ready to go deeper? Check out what’s next:
 
 - 🧠 **Understand the design** and core concepts in the [library overview](overview.md).
 
+- 🔤 **[Learn more about Extension Properties](extensionPropertiesApi.md)**  
+  and make working with your data both convenient and type-safe.
+
 - 💡 **[Use Kotlin DataFrame Compiler Plugin](Compiler-Plugin.md)**  
   for auto-generated column access in your IntelliJ IDEA projects.