Set up Copilot instructions for repository

[Copilot]

Description

Adds .github/copilot-instructions.md to configure GitHub Copilot Coding Agent for this repository per best practices at gh.io/copilot-coding-agent-tips.

Changes

Created comprehensive instructions covering:

• Project structure (Jekyll/Ruby static site for testing conferences)
• Build commands (Docker local dev via ./devops/setup.sh + CircleCI pipeline)
• Data schema for conference YAML entries with required/optional fields and real examples
• Conference eligibility criteria (testing-focused only)
• Code style conventions (2-space YAML, prettier formatting, UTM tracking on URLs)
• Common workflows (adding conferences, moving to past list, updating entries)

Key guidelines for Copilot:

# Example conference entry format
- name: Automation Guild 2026
  location: Online
  dates: "February 9-13, 2026"
  url: https://testguild.com/ag-2026/?utm_source=testingconferences
  twitter: testguilds
  status: <a href="..." target="_blank">Registration is Open</a>

Checklist

• Instructions file created at .github/copilot-instructions.md
• Formatted with prettier
• Code review passed
• Follows GitHub Copilot best practices

Additional context

Enables Copilot to understand repository-specific conventions: YAML data schema, chronological ordering requirements, conference eligibility rules, and proper build/test commands.

Original prompt

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This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #834

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