README.md issue: docker-compose commands fails if following the instructions verbatim

In README.md, when following the steps to install the dependencies, one reaches this:

```
docker volume create --name=uta_vol
docker volume create --name=seqrepo_vol
docker-compose up
```

but there's nothing in the README telling you to have checked out the vrs-python repo at that point.  Without a docker-compose.yml, the docker-compose command fails.