feat(RHINENG-5460): Add rh-pre-commit installation instructions to README

[kruai]

Overview

This PR is being created to address RHINENG-5460.
It adds a note to our Contributing section instructing users to install rh-pre-commit before contributing. I specified that this only applies if you're on the RH network, because rh-pre-commit only works when you're on the VPN.

PR Checklist

• Keep PR title short, ideally under 72 characters
• Descriptive comments provided in complex code blocks
• Tests: validate optimal/expected output
• Tests: validate exceptions and failure scenarios
• Tests: edge cases
• Recovers or fails gracefully during potential resource outages (e.g. DB, Kafka)
• Uses type hinting, if convenient
• Documentation, if this PR changes the way other services interact with host inventory
• Links to related PRs

Secure Coding Practices Documentation Reference

You can find documentation on this checklist here.

Secure Coding Checklist

• Input Validation
• Output Encoding
• Authentication and Password Management
• Session Management
• Access Control
• Cryptographic Practices
• Error Handling and Logging
• Data Protection
• Communication Security
• System Configuration
• Database Security
• File Management
• Memory Management
• General Coding Practices

[thearifismail]

LGTM