Fix file path resolution to use GitHub root path

[joshuavial]

Related to #7 (testing out copilot workspace)

Implements functionality to correctly handle file paths relative to the GitHub root path in the Aider Plugin for Neovim.

• Determines GitHub root path: Adds a function get_git_root_path in lua/aider.lua that determines the GitHub root path using git rev-parse --show-toplevel.
• Adjusts file paths: Modifies AiderOpen, AiderOnBufferOpen, and AiderOnBufferClose functions to prepend the GitHub root path to file paths before adding or managing them. This ensures that file paths are handled correctly when opened from outside the GitHub root.
• Updates documentation: Enhances the README.md to include information on how the plugin now handles file paths relative to the GitHub root path, ensuring users are aware of the new functionality.

---

For more details, open the Copilot Workspace session.

[ikusteu]

Any plans on merging this? I love using the tool, but this resolution issue gets really annoying (especially on JS monorepos with nvim using the root of the package as cwd, for a reason)

[joshuavial]

I think this may be resolved with aider's new handling of file paths - will test more locally