Bug report

Describe the bug
I followed the directions in readme.md for running app via Docker but it did not work. Suspect documentation just needs to be adjusted.

How we reproduce the bug
Steps to reproduce the behaviour:

1. docker pull ghcr.io/mobilitydata/gtfs-validator
2. docker run -v /myDirectory:/theContainerDirectory -it ghcr.io/mobilitydata/gtfs-validator:latest (with appropriate substitutions)
3. java -jar gtfs-validator-v-snapshot_cli.jar -u https://content.amtrak.com/content/gtfs/GTFS.zip (or whatever .zip)_

Expected behaviour
Runs validator on specified URL or file.

Observed behaviour
Opens a Java command line // which failes with the java -jar command.

Environment versions

• validator version: as specified in Dockerfile
• Java version: as specified in Dockerfile
• OS versions: OSX 11.6.4