Add docs mirtop

[atrigila]

Improve docs regarding input files from MirgeneDB

PR checklist

• [x] 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/smrnaseq 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.
• [x] CHANGELOG.md is updated.
• [ ] README.md is updated (including new tool citations and authors/contributors).

[nschcolnicov]

Hi @atrigila, I already updated the mirgenedb hairpin file: https://github.com/nf-core/test-datasets/blob/smrnaseq/MirGeneDB/mirgenedb_hsa_hairpin.fa. This was what was causing the issue https://github.com/nf-core/smrnaseq/issues/477. Apparently we had the wrong links from the start https://github.com/nf-core/smrnaseq/commit/d5500c31eb7ab8ebf7524f055a882729d21f3b83. Or are you referring to something else?