docs: add E2B research badge

Author: simonucl

README.md

@@ -3,6 +3,8 @@
 <h1>Shepherd: Programmable Meta-Agents via Reversible Execution Traces</h1>
 
 ![Status: Alpha](https://img.shields.io/badge/status-alpha-orange?style=for-the-badge) [![PyPI](https://img.shields.io/pypi/v/shepherd-ai?style=for-the-badge&logo=pypi&logoColor=white)](https://pypi.org/project/shepherd-ai/) [![Python](https://img.shields.io/pypi/pyversions/shepherd-ai?style=for-the-badge&logo=python&logoColor=white&label=)](https://pypi.org/project/shepherd-ai/) [![Homepage](https://img.shields.io/badge/Homepage-4d8cd8?style=for-the-badge&logo=google-chrome&logoColor=white)](https://shepherd-agents.ai/) [![Docs](https://img.shields.io/badge/Docs-4d8cd8?style=for-the-badge&logo=materialformkdocs&logoColor=white)](https://docs.shepherd-agents.ai/) [![Paper](https://img.shields.io/badge/Paper-2605.10913-red?style=for-the-badge)](https://arxiv.org/abs/2605.10913) [![Blog](https://img.shields.io/badge/Blog-4d8cd8?style=for-the-badge)](https://shepherd-agents.ai/blog)
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+[![SPONSORED BY E2B FOR RESEARCH](https://img.shields.io/badge/SPONSORED%20BY-E2B%20FOR%20RESEARCH-ff8800?style=for-the-badge)](https://e2b.dev/research)
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