Add Docker Image

[colbyford]

This PR includes a Dockerfile, a simplified conda .yaml file, and an updated README.md that describes how to run FlowDock from inside the container.

I have pushed the Docker image to Docker Hub: https://hub.docker.com/repository/docker/cford38/flowdock

Notes:

• We need to further simplify the environments/flowdock_environment_docker.yaml file to generalize the versions needed of each library. This current conda environment took hours to solve, likely due to the overly specific versions described in the .yaml file.
• This has been tested on the inferencing functionality (python flowdock/sample.py ...) and inferences well with CUDA acceleration. However, it has not been tested on the training or evaluation FlowDock tasks.
• This Docker image does not contain the checkpoints as it is already quite large (>12GB). Thus, users will need to download the desired checkpoint locally and run the Docker image with the local checkpoint directory mounted as a volume.

[amorehead]

Thanks a ton for your contributions here, @colbyford!