Add some launch docs

[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 --paired_end).
• Make sure your code lints (nf-core lint .).
• Documentation in docs is updated
• CHANGELOG.md is updated
• README.md is updated

[jfy133]

Made (e.g. main README) and suggested a couple of tweaks. Please also check MD linting!