Fix docker tagging and add CI/CD docs

[gene1wood]

Fixed

• Docker image tagging for git version tag builds

Previously when tagging a commit, the AWS CodeBuild process would fail with the error

Successfully built 57638a88000c
Successfully tagged mozdef/mozdef_alertactions:latest
cloudy_mozdef/ci/docker_tag_or_push tag v1.38.3
"docker tag" requires exactly 2 arguments.
See 'docker tag --help'.
Usage:  docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]
Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE 

Added

• Documentation on the CI/CD process