docs: add Freshness-Aware-PER to Notable work based on ROLLUpdate README.md

[histmeisah]

Hi ROLL team 👋

This PR adds our paper Freshness-Aware Prioritized Experience Replay for LLM/VLM Reinforcement Learning to the "Notable work based on ROLL" section.

Code (built on top of ROLL): https://github.com/Vision-CAIR/Freshness-Aware-PER

Brief summary:

• reward_fresh priority combining |reward| with exponential age decay
• Asynchronous full-buffer priority refresh (refresh_all_age_decay) so unsampled old entries stay properly decayed
• Episode-indexed n-step / hierarchical sampling for both step-level and trajectory-level buffers
• Apache 2.0, identical to upstream

Happy to adjust wording, ordering, or description length to match the section's style — thanks for the great library!

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