Add SUPPORT.md file with bug report guidance

SUPPORT.md

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+# Support
+
+## Getting Help
+
+If you encounter issues with the GitHub Copilot Token Tracker extension, the best way to get support is by creating a well-documented bug report in the [GitHub Issues](https://github.com/rajbos/github-copilot-token-usage/issues) section of this repository.
+
+## How to Report a Bug
+
+When creating a new issue, please include the following information to help us understand and resolve your problem quickly:
+
+### Required Information
+
+- **VS Code Version**: Help > About (e.g., Version: 1.95.0)
+- **Extension Version**: Check in Extensions view or Help > About
+- **Operating System**: Windows, macOS, or Linux with version
+- **Issue Description**: Clear description of what's happening vs. what you expected
+
+### Helpful Details
+
+- **Steps to Reproduce**: Detailed steps to recreate the issue
+- **Screenshots**: If applicable, include screenshots of the problem
+- **Log Files**: Any relevant error messages from VS Code Developer Console (Help > Toggle Developer Tools)
+- **Token Usage Data**: Mention if the issue relates to specific token counts or model usage
+
+### Known Limitations
+
+Before reporting, please check if your issue is related to these known limitations mentioned in the README:
+
+- Numbers are based on local log files only (multi-machine usage not tracked)
+- Premium Requests are not tracked
+- Token counts are estimates based on character count
+- Extension currently tested primarily on Windows
+
+## Feature Requests
+
+Feature requests are also welcome! Please use the same issue tracker and clearly label your request as a feature request with a detailed description of the proposed functionality.
+
+## Contributing
+
+If you're interested in contributing to the project, please check for existing issues or create a new one to discuss your proposed changes before submitting a pull request.