Add Dockerfile and requirements

[AlekseyLobanov]

Hello.

Industry standard for applications deployment is docker (or OCI containers).
Fixed (at least on top level) requirements also is a good practice for projects without active development.

For simple build & run you can use this:

docker build --tag greedy .
docker run --name greedy -p 8000:5000 --rm greedy

Unfortunately, I get this error in a working application.