This patch updates the main Dockerfile container build to use
the python:3.8-slim base image and installs aprsd from pypi.
This also results in a much smaller image.
Also added support for multiarchitecture builds so the same Dockerfile
builds for raspberry pi and linux/amd64
This patch updates the 2 readme files with copies for the latest
sample-config output to match the 1.6.0 release's config.
Also fixed a small issue with the Dockerfile.