Updates README with Docker build instructions

Author: ryanprior

README.md

@@ -12,28 +12,44 @@ zlib1g-dev
 ```
 
 We recommend installing gems to a (hidden) directory in your home folder:
-```bash
-echo '' >> ~/.bashrc
-echo '# Install Ruby Gems to ~/.gems' >> ~/.bashrc
-echo 'export GEM_HOME="$HOME/.gems"' >> ~/.bashrc
-echo 'export PATH="$HOME/.gems/bin:$PATH"' >> ~/.bashrc
-echo '' >> ~/.bashrc
-source ~/.bashrc
+```sh-session
+$ echo '' >> ~/.bashrc
+$ echo '# Install Ruby Gems to ~/.gems' >> ~/.bashrc
+$ echo 'export GEM_HOME="$HOME/.gems"' >> ~/.bashrc
+$ echo 'export PATH="$HOME/.gems/bin:$PATH"' >> ~/.bashrc
+$ echo '' >> ~/.bashrc
+$ source ~/.bashrc
 ```
 
 Install jekyll and bundler:
-```bash
-gem install jekyll bundler
+```sh-session
+$ gem install jekyll bundler
 ```
 
 Install gems:
-```bash
-bundle install
+```sh-session
+$ bundle install
 ```
 
 Build and serve locally with:
-```bash
-bundle exec jekyll serve --host 0.0.0.0
+```sh-session
+$ bundle exec jekyll serve --host 0.0.0.0
 ```
 
 The site should now be available at http://0.0.0.0:4000/ on your local machine, and your local machine's IP address on your network—great for testing on mobile OSes.
+
+### Alternative: building with Docker
+
+You'll need Docker installed on your system.
+
+Build the Docker image:
+```sh-session
+$ bin/build-container
+```
+
+Build and serve locally with:
+```sh-session
+$ bin/serve
+```
+
+The site should now be available at http://0.0.0.0:4000/