Document the docker tool

[ahwagner]

Our getting started section provides guidance on spinning up dependent services (e.g. seqrepo) using Docker, but doesn't mention what Docker is. This is assumed knowledge for most of us but it is possible that people coming in may not have used Docker before. It would be helpful to minimally point to the Docker getting started docs.

[github-actions]

This issue was marked stale due to inactivity.

[kehshiba]

can you assign me on this ?

[ahwagner]

@kehshiba by all means, please feel free to work on this issue!

[kehshiba]

@ahwagner updating the readme is enough?

[ahwagner]

I think that's a good starting place and sufficient for resolving this issue.

[kehshiba]

@ahwagner #188 fixes this, can you check?