Expand README

[erinyoung]

This looks like it's going to be cool!

I, however, don't know how I'm expected to run this workflow. My prior experience with NextStrain builds is that I gave it

1. a multifasta fasta file
2. a metadata file
3. 10 million config files

How are you hoping this workflow works?

[jwarnn]

My idea was that a user could make a very basic tree then build on features available from Nextstrain to fit their use case. This would involve figuring out runtime parameters for the Nextflow script like params.sequences_per_group then eventually passing the script the more detailed config files, i.e. auspice_config, lat_longs, and colors. I am going to work on the README to explain how to use what I have currently in the repository and what I am looking to add.

[jwarnn]

PR #4 began to address this issue. The README can still be much improved; leaving the issue open so suggestions for improvement to the README have a place to live.