Swing tutorial jar comment

[smclacke]

Added a comment to the swingset3 tutorial to clarify the app we use causes harmless errors.

[GabrielaReyna]

I am taking a look to this now. I might come with further instructions.

[GabrielaReyna]

Hi Sarah, thanks for taking a look at this.

I'd like for you to do the following in this PR:

• I believe some of the jars in the swingset tutorial are empty and not needed. Please test this out and get rid of unnecessary files. These changes should apply to the zip file in the tutorial, the examples folder in the cheerpj-meta repo and in the swingset3 leaning tech repo ( the one deployed and used in the tutorial iframe). If you have checked all of this, feel free to just ignore this bullet point.
• The zip files in all the tutorials of cheerpj contain the HTML file where cheerpj is loaded via the loader URL. This is a pain to update every single time there is a new version, zip back and modify the tutorials. Hence, please modify the tutorial's HTML file and replace the loader URL with "paste url here" maybe pointing to a url in the docs with the current loader URL. Please do for all the cheerpj tutorials that have a downloadable layout.
• Once the bullet point above is complete, please mention in the tutorials that the url needs to be updated.

If you have a better suggestion on how to do the above, for example, automating creating a zip that exists in the examples repo rather than in the labs repo would be amazing. But if not, the simple solution above should be enough.

Many thanks!