Add changelog and fix for issue with index

[apeltzer]

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 necessary, also make a PR on the nf-core/eager branch on the nf-core/test-datasets repo
• Ensure the test suite passes (nextflow run . -profile test,docker).
• Make sure your code lints (nf-core lint .).
• Documentation in docs is updated
• CHANGELOG.md is updated
• README.md is updated

[drpatelh]

You will need to do the same here too @apeltzer 👍

eager/main.nf

Line 824 in 2f0621f

file index from bwa_index_bwamem