Update README.md with star history (#35)

Author: evanotero

README.md

@@ -91,3 +91,7 @@ The Security extension scans files for the following vulnerabilities:
 
 - License: [Apache License 2.0](https://github.com/gemini-cli-extensions/security/blob/main/LICENSE)
 - Security: [Security Policy](https://github.com/gemini-cli-extensions/security/blob/main/SECURITY.md)
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+## Star history
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+[![Star History Chart](https://api.star-history.com/svg?repos=gemini-cli-extensions/security&type=Date)](https://www.star-history.com/#gemini-cli-extensions/security&Date)