Modified single_cell_tutorial.md and added files needed for the tutorials

[Vivian0105]

PR checklist

• This comment contains a description of changes (with reason).
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added a new tool - have you followed the pipeline conventions in the contribution docs
• If necessary, also make a PR on the nf-core/airrflow branch on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core pipelines lint).
• Ensure the test suite passes (nextflow run . -profile test,docker --outdir <OUTDIR>).
• Check for unexpected warnings in debug mode (nextflow run . -profile debug,test,docker --outdir <OUTDIR>).
• Usage Documentation in docs/usage.md is updated.
• Output Documentation in docs/output.md is updated.
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).

[github-actions]

Warning

Newer version of the nf-core template is available.

Your pipeline is using an old version of the nf-core template: 3.0.2.
Please update your pipeline to the latest version.

For more documentation on how to update your pipeline, please see the nf-core documentation and Synchronisation documentation.

[ggabernet]

Thanks for your contributions @Vivian0105, I see your changes and I've added some comments so far. You can continue working on this branch and pushing commits and once the tutorial is ready we'll merge the PR :)

[ggabernet]

This file seems to be empty, can it be removed?

[ggabernet]

I don't think that we need to provide this command as a separate file, as it is very simple, I would just add it as a command in the tutorial Markdown file