doc: add rust install instructions

[rithulkamesh]

Motivation and Context

This PR adds detailed instructions for installing Rust. With recent updates requiring Rust tooling, these instructions will help users quickly set up Rust for local development, ensuring compatibility with our project's build and runtime environments.

How Has This Been Tested?

The installation steps have been manually verified on multiple operating systems using the official installer (rustup). After installation, running "rustc --version" confirmed the correct version for our requirements.

Breaking Changes

No breaking changes. The update exclusively supplements our documentation and does not alter existing setup instructions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the Codellm-Devkit Documentation
• My changes adhere to the repository's style guidelines
• New and existing tests pass locally
• I have added or updated documentation as needed

Additional context

The new instructions leverage rustup for installation, addressing both newcomers and experienced Rust developers. For more details, refer to the official Rust documentation.