Compute checksum for each input file

[delfiterradas]

Closes #30:

• Install md5sum module
• Install shasum module
• Compute checksum for each input file
• Update samplesheet
• Update test

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/datasync 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).

[atrigila]

Good first implementation. We will iterate on this so that it can accept an s3 directory and a checksum tsv.
Please add changelog to this one. Thanks!