adding README and Dockerfile for Github actions, will test with my branch

Author: vsoch

actions/Dockerfile

@@ -0,0 +1,44 @@
+FROM golang:1.11.3-stretch
+
+# docker build -f actions/Dockerfile -t googlecontainertools/container-diff .
+
+RUN apt-get update && \
+    apt-get install -y automake \
+                       libffi-dev \ 
+                       libxml2 \
+                       libxml2-dev \
+                       libxslt-dev \
+                       libxslt1-dev \
+                       git \
+                       gcc g++ \
+                       wget \
+                       locales
+
+RUN sed -i -e 's/# en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' /etc/locale.gen && \
+    locale-gen
+ENV LANG en_US.UTF-8  
+ENV LANGUAGE en_US:en  
+ENV LC_ALL en_US.UTF-8
+
+LABEL "com.github.actions.name"="container-diff GitHub Action"
+LABEL "com.github.actions.description"="use Container-Diff in Github Actions Workflows"
+LABEL "com.github.actions.icon"="cloud"
+LABEL "com.github.actions.color"="blue"
+
+LABEL "repository"="https://www.github.com/GoogleContainerTools/container-diff"
+LABEL "homepage"="https://www.github.com/GoogleContainerTools/container-diff"
+LABEL "maintainer"="Google Inc."
+
+# Install container-diff from master
+RUN go get github.com/GoogleContainerTools/container-diff && \
+    cd ${GOPATH}/src/github.com/GoogleContainerTools/container-diff && \
+    go get && \
+    make && \
+    go install && \
+    mkdir -p /code && \
+    apt-get autoremove
+
+RUN mkdir -p /root/.docker && \
+    echo {} > /root/.docker/config.json
+
+ENTRYPOINT ["container-diff"]

actions/README.md

@@ -0,0 +1,79 @@
+# Container Diff for Github Actions
+
+This is a Github Action to allow you to run Container Diff in a 
+[Github Actions](https://help.github.com/articles/about-github-actions/#about-github-actions)
+workflow. The intended use case is to build a Docker container from the repository,
+push it to Docker Hub, and then use container-diff to extract metadata for it that
+you can use in other workflows (such as deploying to Github pages). In
+the example below, we will show you how to build a container, push
+to Docker Hub, and then container diff.  Here is the entire workflow:
+
+## Example 1: Run Container Diff
+
+Given an existing container on Docker Hub, we can run container diff
+without doing any kind of build.
+
+```
+workflow "Run container-diff" {
+  on = "push"
+  resolves = ["list"]
+}
+
+action "Run container-diff" {
+  args = ["analyze", "vanessa/salad", "--type=pip", "type=apt", "--type=history", --output "/github/workspace/data.json", "--type=file", "--json", "--quiet", "--verbosity=panic" ]
+}
+
+action "list" {
+  needs = ["Run container-diff"]
+  uses = "actions/bin/sh@master"
+  runs = "ls"
+  args = ["/github/workspace"]
+}
+```
+
+In the above, we run container-diff to output apt and pip packages, history,
+and the filesystem for the container "vanessa/salad" that already exists on
+Docker Hub. We save the result to a data.json output file. The final step in 
+the workflow (list) is a courtesy to show that the data.json file is generated.
+
+## Example 2: Build, Deploy, Run Container Diff
+
+This next example is slightly more complicated in that it will run container-diff
+after a container is built and deployed from a Dockerfile present in the repository.
+
+```
+workflow "Run container-diff after deploy" {
+  on = "push"
+  resolves = ["Run container-diff"]
+}
+
+action "build" {
+  uses = "actions/docker/cli@master"
+  args = "build -t vanessa/salad ."
+}
+
+action "login" {
+  uses = "actions/docker/login@master"
+  secrets = ["DOCKER_USERNAME", "DOCKER_PASSWORD"]
+}
+
+action "push" {
+  uses = "actions/docker/cli@master"
+  args = "push vanessa/salad"
+}
+
+action "Run container-diff" {
+  needs = ["build", "login", "push"]
+  args = ["analyze", "vanessa/salad", "--type=pip", "type=apt", "--type=history", --output "/github/workspace/data.json", "--type=file", "--json", "--quiet", "--verbosity=panic" ]
+}
+
+action "list" {
+  needs = ["Run container-diff"]
+  uses = "actions/bin/sh@master"
+  runs = "ls"
+  args = ["/github/workspace"]
+}
+```
+
+The intended use case of the above would be to, whenever you update your
+container, deploy its metadata to Github pages (or elsewhere).