fix: Missing instructions in goose/CONTRIBUTING.md

[github-actions]

Closes #6517

Summary

Summary of Changes for Issue #6517

Issue: Missing instructions in goose/CONTRIBUTING.md

Changes Made

1. Added hermit environment activation instruction

Added source bin/activate-hermit before cargo build in the "Getting Started > Rust" section. This is the missing instruction that new contributors need to set up their development environment.

2. Improved tone and formality

Rephrased multiple sections in the "Getting Started" area to reduce informal "you" usage:

• "First let's compile goose and try it out" → "First, activate the hermit environment and compile goose"
• "you should now have debug builds" → "debug builds of the binaries are available"
• "If you haven't used the CLI before, you can use this" → "For first-time setup, run the configure command"
• "once you have a connection to an LLM provider working, you can run a session!" → "Once a connection to an LLM provider is working, start a session"
• "As you make changes to the rust code, you can try it out" → "When making changes to the Rust code, test them"
• "Now let's make sure you can run the app" → "To run the app"
• "You should see the app open a window" → "The app opens a window"
• "You can now make changes in the code" → "Changes to the GUI can be made"
• Similar improvements in the Regenerating OpenAPI and Debugging sections

Files Modified

• CONTRIBUTING.md (1 file, 20 insertions, 21 deletions)

Verification

• Document structure preserved
• Instructions remain clear for new contributors
• Markdown formatting maintained

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Pull request overview

This PR fixes missing hermit environment activation instructions in CONTRIBUTING.md and improves the documentation tone.

Changes:

• Added source bin/activate-hermit command before cargo build in the Rust setup section
• Improved tone throughout Getting Started section by reducing informal language and making instructions more direct