Update news of Nemotron=3-Super is supported on Megatron-Bridge (#1025)

### What does this PR do?

Type of change: Documentation

Add Nemotron-3-Super launch news entries to the README "Latest News"
section:

A new entry highlighting that [NeMo Megatron
Bridge](https://github.com/NVIDIA-NeMo/Megatron-Bridge) now supports
Nemotron-3-Super quantization (PTQ) and export workflows using the Model
Optimizer library, with a link to the [Quantization (PTQ and QAT)
guide](https://github.com/NVIDIA-NeMo/Megatron-Bridge/blob/super-v3/docs/models/llm/nemotron3-super.md#quantization-ptq-and-qat).

### Usage

```markdown
N/A — documentation-only change (README.md update).
```

### Testing

No testing required; this is a documentation-only change to README.md.

### Before your PR is "*Ready for review*"

Make sure you read and follow [Contributor
guidelines](https://github.com/NVIDIA/Model-Optimizer/blob/main/CONTRIBUTING.md)
and your commits are signed (`git commit -s -S`).

Make sure you read and follow the [Security Best
Practices](https://github.com/NVIDIA/Model-Optimizer/blob/main/SECURITY.md#security-coding-practices-for-contributors)
(e.g. avoiding hardcoded `trust_remote_code=True`, `torch.load(...,
weights_only=False)`, `pickle`, etc.).

- Is this change backward compatible?: N/A
- If you copied code from any other sources or added a new PIP
dependency, did you follow guidance in `CONTRIBUTING.md`: N/A
- Did you write any new necessary tests?: N/A
- Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?:
N/A

### Additional Information

Related links:
- Megatron Bridge Nemotron 3 Super docs:
https://github.com/NVIDIA-NeMo/Megatron-Bridge/blob/super-v3/docs/models/llm/nemotron3-super.md

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Updated latest news section with announcement of March 2026 release:
NeMo Megatron Bridge now provides full support for Nemotron-3-Super
quantization capabilities, supporting both Post-Training Quantization
(PTQ) and Quantization-Aware Training (QAT) approaches
* Added detailed documentation covering export workflows via the Model
Optimizer library with direct reference links to comprehensive
quantization guides

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: James Shen <yueshen@nvidia.com>

Author: yueshen2016

README.md

@@ -27,6 +27,7 @@ Model Optimizer is also integrated with [NVIDIA Megatron-Bridge](https://github.
 ## Latest News
 
 - [2026/03/11] Model Optimizer quantized Nemotron-3-Super checkpoints are available on Hugging Face for download: [FP8](https://huggingface.co/nvidia/NVIDIA-Nemotron-3-Super-120B-A12B-FP8), [NVFP4](https://huggingface.co/nvidia/NVIDIA-Nemotron-3-Super-120B-A12B-NVFP4). Learn more in the [Nemotron 3 Super release blog](https://blogs.nvidia.com/blog/nemotron-3-super-agentic-ai/). Check out how to quantize Nemotorn 3 models for deployment acceleration [here](./examples/llm_ptq/README.md)
+- [2026/03/11] [NeMo Megatron Bridge](https://github.com/NVIDIA-NeMo/Megatron-Bridge) now supports Nemotron-3-Super quantization (PTQ and QAT) and export workflows using the Model Optimizer library. See the [Quantization (PTQ and QAT) guide](https://github.com/NVIDIA-NeMo/Megatron-Bridge/blob/super-v3/docs/models/llm/nemotron3-super.md#quantization-ptq-and-qat) for FP8/NVFP4 quantization and HF export instructions.
 - [2025/12/11] [BLOG: Top 5 AI Model Optimization Techniques for Faster, Smarter Inference](https://developer.nvidia.com/blog/top-5-ai-model-optimization-techniques-for-faster-smarter-inference/)
 - [2025/12/08] NVIDIA TensorRT Model Optimizer is now officially rebranded as NVIDIA Model Optimizer.
 - [2025/10/07] [BLOG: Pruning and Distilling LLMs Using NVIDIA Model Optimizer](https://developer.nvidia.com/blog/pruning-and-distilling-llms-using-nvidia-tensorrt-model-optimizer/)