Update README.md install instructions, add Docker support.

Dockerfile

@@ -0,0 +1,9 @@
+FROM ruby:2.3
+
+# jekyll_pages_api_search needs Node, so we gotta install it.
+
+# https://nodejs.org/en/download/package-manager/
+
+RUN apt-get update && \
+    curl -sL https://deb.nodesource.com/setup_6.x | bash - && \
+    apt-get install -y nodejs zip

README.md

@@ -26,17 +26,42 @@ We started by adapting [GOV.UK’s work](https://www.gov.uk/guidance/content-des
 
 ### Running the site
 
-The 18F Content Guide runs on [Jekyll](http://jekyllrb.com/). To run it locally:
+The 18F Content Guide runs on [Jekyll](http://jekyllrb.com/).
 
+To run it locally:
+
+1. Make sure that you have Ruby 2.3. At present, this project is incompatible with Ruby 2.4.
 1. Clone the repository.
-1. Get [Jekyll] and the necessary dependencies: `bundle install`
+1. Get [Jekyll][] and the necessary dependencies: `bundle install`
 1. Run the web server with `./go serve` (or `jekyll serve` if you have Jekyll installed globally)
 1. Visit the local site at [http://localhost:4000](http://localhost:4000)
 
+Note that you will also need [Node.js][] in order for the site's built-in
+search functionality to work. If you don't have it, that's ok--the search
+functionality won't work for you, though.
+
+### Running the site with Docker
+
+If you don't want to have to deal with making sure that you have the
+proper version of Ruby and Node installed, you can use Docker instead. It
+takes care of all the dependencies for you.
+
+1. Install [Docker][].
+1. Clone the repository.
+1. Run `docker-compose up`.
+1. Visit the local site at [http://localhost:4000](http://localhost:4000)
+
+If you ever decide that you no longer want to use Docker, run
+`docker-compose down -v` to properly clean everything up.
+
 ### Public domain
 
 This project is in the worldwide [public domain](LICENSE.md).
 
 > As a work of the United States government, this project is in the public domain within the United States.
 
 > Additionally, we waive copyright and related rights in the work worldwide through the CC0 1.0 Universal public domain dedication.
+
+[Jekyll]: http://jekyllrb.com/
+[Node.js]: https://nodejs.org/en/
+[Docker]: https://www.docker.com/

docker-compose.yml

@@ -0,0 +1,16 @@
+version: '2'
+services:
+  app:
+    build: .
+    working_dir: /content-guide
+    command: bash -c 'bundle install && jekyll serve --force_polling -H 0.0.0.0 -P 4000'
+    stop_signal: SIGKILL
+    ports:
+      - 4000:4000
+    volumes:
+      - .:/content-guide
+      - root:/root/
+      - bundle:/usr/local/bundle/
+volumes:
+  root:
+  bundle: