PYTHON-5742 - Add Copilot instructions (#2717)

Author: NoahStapp

.github/copilot-instructions.md

@@ -0,0 +1,44 @@
+When reviewing code, focus on:
+
+## Security Critical Issues
+- Check for hardcoded secrets, API keys, or credentials.
+- Check for instances of potential method call injection, dynamic code execution, symbol injection or other code injection vulnerabilities.
+
+## Performance Red Flags
+- Spot inefficient loops and algorithmic issues.
+- Check for memory leaks and resource cleanup.
+
+## Code Quality Essentials
+- Methods should be focused and appropriately sized. If a method is doing too much, suggest refactorings to split it up.
+- Use clear, descriptive naming conventions.
+- Avoid encapsulation violations and ensure proper separation of concerns.
+- All public classes, modules, and methods should have clear documentation in Sphinx format.
+
+## PyMongo-specific Concerns
+- Do not review files within `pymongo/synchronous` or files in `test/` that also have a file of the same name in `test/asynchronous` unless the reviewed changes include a `_IS_SYNC` statement. PyMongo generates these files from `pymongo/asynchronous` and `test/asynchronous` using `tools/synchro.py`.
+- All asynchronous functions must not call any blocking I/O.
+
+## Review Style
+- Be specific and actionable in feedback.
+- Explain the "why" behind recommendations.
+- Acknowledge good patterns when you see them.
+- Ask clarifying questions when code intent is unclear.
+
+Always prioritize security vulnerabilities and performance issues that could impact users.
+
+Always suggest changes to improve readability and testability. For example, this suggestion seeks to make the code more readable, reusable, and testable:
+
+```python
+# Instead of:
+if user.email and "@" in user.email and len(user.email) > 5:
+    submit_button.enabled = True
+else:
+    submit_button.enabled = False
+
+# Consider:
+def valid_email(email):
+    return email and "@" in email and len(email) > 5
+
+
+submit_button.enabled = valid_email(user.email)
+```