Broken link in contributing.md

The contributing.md file has a broken link for development instructions: [Contributing.md](https://github.com/agent0ai/agent-zero/blob/main/docs/guides/contribution.md#:~:text=See%20development%20for%20instructions%20on%20how%20to%20set%20up%20a%20development%20environment).

The file either got renamed or deleted and the reference to it wasn't updated. 