Add user to container to support running as non-root

[kinghrothgar]

Running docker containers as root in production is not good security practice for a lot of reasons. It is difficult to use the images provide without running as root there is no user to run it as. This PR adds a user so that one can run hound as non-root.

I did not change the default user of the container so this should have no effect on those already utilizing the container and expecting it to run as root.

This will allow one to easily run the container as non-root with Docker, Kuberntes, etc (See README change).

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [x] Feature
• [ ] Code style update
• [ ] Refactor
• [x] Build-related changes
• [ ] Other, please describe:

The PR fulfills these requirements:

• [x] All tests are passing?
• [ ] New/updated tests are included?
• [ ] If any static assets have been updated, has ui/bindata.go been regenerated?
• [ ] Are there doc blocks for functions that I updated/created?

If adding a new feature, the PR's description includes:

• [x] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information: