Report location of MultiQC output

[jfy133]

Is your feature request related to a problem? Please describe

Some new user to the pipeline are not familiar with what to do when they get their results. In particular, where to find the run report.

We should add a little message on completetion where a user can find their multiQC run report.

Describe the solution you'd like

Originally proposed by @mahesh-panchal on slack

Could do something along the lines of:

https://github.com/nf-core/viralrecon/blob/0d25be11aa2d1e99a469418c2b0ef35773503c4e/workflows/sra_download.nf#L107
https://github.com/nf-core/viralrecon/blob/0d25be11aa2d1e99a469418c2b0ef35773503c4e/lib/Workflow.groovy#L300-L310

Describe alternatives you've considered

Additional context