Add Dockerfile and instructions for running container

Dockerfile

@@ -0,0 +1,10 @@
+FROM python:3-alpine
+
+WORKDIR /usr/src/app
+
+COPY docker-net-graph.py Pipfile Pipfile.lock ./
+
+RUN pip install pipenv
+RUN pipenv install --system --deploy
+
+CMD ["python", "docker-net-graph.py"]

README.md

@@ -20,4 +20,15 @@ In most cases what you want to run are the following couple commands:
     pipenv install
     pipenv run python docker-net-graph.py -o output.gv
 
-This will end up generating a .pdf file containing the graph.
+This will end up generating a .pdf file containing the graph.
+
+## Running inside docker
+If you want to generate a graph for a remote system you can also easily
+run this script inside a pre-built docker container:
+    
+    docker run -v /var/run/docker.sock:/var/run/docker.sock leoverto/docker-net-graph
+
+This will just generate and output the graph. You can then run
+`dot -Tpdf -o out.pdf`or `dot -Tpng -o out.png` on a system with
+graphviz installed, paste the previous output there, press enter
+and finally CTRL+C to generate the file.