Add upstream DiT MIT license information

The model card currently omits license metadata and the repository has no license file. This adds the MIT license information from the upstream [Microsoft UniLM DiT project](https://github.com/microsoft/unilm/tree/31c5b904ca1bf2afb4c234a6675c683a4e5fc7cd/dit).

- Add `license: mit` to the model-card metadata.
- Add the upstream MIT `LICENSE`, preserving Microsoft's copyright notice and the full license text (line endings normalized to LF).
- Add a model-card License section linking to the local license and its pinned upstream source.

Source: [UniLM LICENSE](https://github.com/microsoft/unilm/blob/31c5b904ca1bf2afb4c234a6675c683a4e5fc7cd/LICENSE). The [upstream README](https://github.com/microsoft/unilm/blob/31c5b904ca1bf2afb4c234a6675c683a4e5fc7cd/README.md#license) identifies this root license as the project license, and DiT has no separate license file.

Validation: Hugging Face model-card validation passed; license content matches the pinned upstream file after normalizing line endings; `git diff --check` passed.

LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) Microsoft Corporation
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -1,4 +1,5 @@
 ---
+license: mit
 tags:
 - dit
 inference: false
@@ -10,6 +11,10 @@ Document Image Transformer (DiT) model pre-trained on IIT-CDIP (Lewis et al., 20
 
 Disclaimer: The team releasing DiT did not write a model card for this model so this model card has been written by the Hugging Face team.
 
+## License
+
+DiT is released under the [MIT License](LICENSE), as provided in the [upstream UniLM repository](https://github.com/microsoft/unilm/blob/31c5b904ca1bf2afb4c234a6675c683a4e5fc7cd/LICENSE). Copyright (c) Microsoft Corporation.
+
 ## Model description
 
 The Document Image Transformer (DiT) is a transformer encoder model (BERT-like) pre-trained on a large collection of images in a self-supervised fashion. The pre-training objective for the model is to predict visual tokens from the encoder of a discrete VAE (dVAE), based on masked patches.
@@ -54,4 +59,4 @@ loss, logits = outputs.loss, outputs.logits
   journal={Proceedings of the 29th annual international ACM SIGIR conference on Research and development in information retrieval},
   year={2006}
 }
-```
+```