Add Containerfile distribution

[rpdelaney]

Is your feature request related to a problem? Please describe.

I don't use ubuntu. Maybe I don't want to install and maintain all those dependencies on my production systems. But I want to use textract.

Solution: Provide a containerized (e.g. Docker) distribution with textract and its dependencies already installed.

Describe alternatives you've considered

None.

Additional context

If you would accept a pull request I can probably do the Containerfile in a short time. If you want a build system in CI and distribution to dockerhub or such, that would be a stretch goal.