update maisi readme (#2018)

Fixes # .

### Description
A few sentences describing the changes proposed in this pull request.

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Avoid including large-size files in the PR.
- [x] Clean up long text outputs from code cells in the notebook.
- [x] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [x] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [x] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

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Signed-off-by: Can Zhao <[email protected]>
Co-authored-by: Can Zhao <[email protected]>

Author: Can-Zhao

generation/maisi/README.md

@@ -20,6 +20,10 @@ We are excited to announce the new MAISI Version `maisi3d-rflow`. Compared with
 - For the released model weights, `maisi3d-rflow` can generate images with better quality for head region and small output volumes than `maisi3d-ddpm`; they have comparable quality for other cases.
 - `maisi3d-rflow` added a diffusion model input `modality`, which gives it flexibility to extend to other modalities. Currently it is set as always equal to 1 since this version only supports CT generation. We predefined some modalities in [./configs/modality_mapping.json](./configs/modality_mapping.json).
 
+More details can be found in our 2025 report:
+
+[Zhao, C., Guo, P., Yang, D., Tang, Y., ... & Xu, D. (2025). MAISI-v2: Accelerated 3D High-Resolution Medical Image Synthesis with Rectified Flow and Region-specific Contrastive Loss](https://arxiv.org/pdf/2508.05772)
+
 **GUI demo:** Welcome to try our GUI demo at [https://build.nvidia.com/nvidia/maisi](https://build.nvidia.com/nvidia/maisi).
 The GUI is only a demo for toy examples. This Github repo is the full version.