Update CONTRIBUTING.md

GitHub allows direct upload of files with a `.csv` suffix now.

.github/CONTRIBUTING.md

@@ -16,7 +16,7 @@ If you think you've encountered a bug in seaborn, please report it on the [Githu
 - A clear explanation of why you think something is wrong
 - The specific versions of seaborn and matplotlib that you are working with
 
-Bug reports are easiest to address if they can be demonstrated using one of the example datasets from the seaborn docs (i.e. with `seaborn.load_dataset`). Otherwise, it is preferable that your example generate synthetic data to reproduce the problem. If you can only demonstrate the issue with your actual dataset, you will need to share it, ideally as a csv. Note that you can upload a csv directly to a github issue thread, but it must have a `.txt` suffix.
+Bug reports are easiest to address if they can be demonstrated using one of the example datasets from the seaborn docs (i.e. with `seaborn.load_dataset`). Otherwise, it is preferable that your example generate synthetic data to reproduce the problem. If you can only demonstrate the issue with your actual dataset, you will need to share it, ideally as a csv (do not share data as a pickle file).
 
 If you've encountered an error, searching the specific text of the message before opening a new issue can often help you solve the problem quickly and avoid making a duplicate report.