Fix Grammar and Clarity Issues in CONTRIBUTING.md and CODE_OF_CONDUCT.md

[klu2300031389]

This PR fixes minor grammatical issues, improves clarity, and updates outdated references in the CONTRIBUTING.md and CODE_OF_CONDUCT.md files.

🔹 Changes Made:
✅ CONTRIBUTING.md:

• Fixed "an LAMP-based" → "a LAMP-based" (correct article usage).
• Corrected "uses a series of Symfony 2 modules" → "use a series of Symfony 2 modules" (subject-verb agreement).
• Improved clarity in Docker setup instructions.

✅ CODE_OF_CONDUCT.md:

• Fixed "pledge to making" → "pledge to make" (correct verb form).
• Added a new section for appeal procedures (contributors can appeal within 30 days).
• Improved clarity in behavior expectations (e.g., defined "inappropriate conduct" more clearly).

📌 Why These Changes Are Needed:
Improves readability and professionalism.
Ensures correct grammar and formatting.
Adds more transparency to the Code of Conduct enforcement process.

[codeclimate]

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[ywarnier]

Thanks. For "behaviour", I prefer the UK-English notation but we don't have a strict policy for this so I accepted it too as it might come from the description of Behat (haven't checked).