add image and update link (#892)

README.md

@@ -125,7 +125,7 @@ The official ML.NET samples are divided in multiple categories depending on the
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   <td align="middle"><img src="images/database.png" alt="Database chart"><br><img src="images/app-type-getting-started-term-cursor.png" alt="Getting started icon"><br><b>Loading data with  LoadFromEnumerable<br><a href="samples/csharp/getting-started/DatabaseIntegration">C#</a><b></td>
   <td align="middle"><img src="images/model-explain-smaller.png" alt="Model explainability chart"><br><img src="images/app-type-e2e-black.png" alt="End-to-end app icon"><br><b>Model Explainability<br><a href="samples/csharp/end-to-end-apps/Model-Explainability">C#</a></b></td>
-  <td align="middle"><img src="images/model-explain-smaller.png" alt="Model explainability chart"><br><img src="images/app-type-e2e-black.png" alt="End-to-end app icon"><br><b>Export to ONNX<br><a href="samples/csharp/getting-started/ONNXExport">C#</a></b></td>
+  <td align="middle"><img src="images/extensibility.png" alt="Extensibility icon"><br><img src="images/app-type-e2e-black.png" alt="End-to-end app icon"><br><b>Export to ONNX<br><a href="samples/csharp/getting-started/Regression_ONNXExport">C#</a></b></td>
   </tr>
 </table>