📝 docs: Review Guide for CFP reviewers on the Pretalx platform

This merge request adds a new guide aimed at providing best practices and guidance for reviewers evaluating Call for Proposal submissions on the Pretalx platform. The guide outlines key evaluation criteria and offers tips for fair and constructive feedback.

Purpose: Help reviewers deliver valuable feedback to speakers, ensuring the selection of high-quality presentations that align with Fedora's values and event goals.

Benefits:

1. Supports a consistent and transparent review process across Fedora events.
2. Assists reviewers in providing actionable feedback to improve proposal submissions.
3. Enhances the overall quality and relevance of selected talks at Fedora events.