Fix URLs (#18604)

Co-authored-by: Niels Rogge <nielsrogge@Nielss-MacBook-Pro.local>

docs/source/en/model_doc/donut.mdx

@@ -33,7 +33,7 @@ This model was contributed by [nielsr](https://huggingface.co/nielsr). The origi
 Tips:
 
 - The quickest way to get started with Donut is by checking the [tutorial
-  notebooks](https://github.com/NielsRogge/Transformers-Tutorials/tree/master/donut), which show how to use the model
+  notebooks](https://github.com/NielsRogge/Transformers-Tutorials/tree/master/Donut), which show how to use the model
   at inference time as well as fine-tuning on custom data.
 - Donut is always used within the [VisionEncoderDecoder](vision-encoder-decoder) framework.
 
@@ -188,7 +188,7 @@ See the [model hub](https://huggingface.co/models?filter=donut) to look for Donu
 
 ## Training
 
-We refer to the [tutorial notebooks](https://github.com/NielsRogge/Transformers-Tutorials/tree/master/donut).
+We refer to the [tutorial notebooks](https://github.com/NielsRogge/Transformers-Tutorials/tree/master/Donut).
 
 ## DonutSwinConfig