Build and publish docker img along with nu plugins

* Add Package.Dockerfile as flexible build source

* Add docker-compose.package.yml as intermediary config

* CI will use new github action YAML format

it only publish the docker image on git tag

* Add debian:latest, debian:slim, and alpine as base image

* Add documentation

docker/Package.Dockerfile

@@ -0,0 +1,5 @@
+ARG base
+FROM ${base}
+
+COPY target/release/nu* /bin/
+ENTRYPOINT ["nu"]

docker/docker-compose.package.yml

@@ -0,0 +1,10 @@
+version: '3'
+
+services:
+  nushell:
+    image: ${REGISTRY}/nu:${TAG}
+    build:
+      context: ..
+      dockerfile: docker/Package.Dockerfile
+      args:
+        base: ${BASE_IMAGE}