Update 05.4_contributing.md

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intermediate/data_cleaning/05.4_contributing.md

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-## Contributing
+# Contributing
 
 This project is an evolving community effort. **We want to hear from you!**. Many workflows involve some version of the examples discussed here. The solutions you've developed in your work could help future users and help the community move toward more established norms around tidy data. Please consider submitting any examples you may have. You can create an issue [here](https://github.com/e-marshall/tidy-xarray/issues/new?assignees=&labels=&projects=&template=data-tidying-example-template.md&title=).If you have any questions or topics you'd like to discuss, please don't hesitate to create an issue on github.