Simple dockerfile that sets up and installs embark and ethereumjs-testrpc, so that you can easily get started building apps with Embark.
Run build, then run shell to get started.
The most basic usage would be something like this:
./build
./shell
embark new my-app
cd my-app
The shell command will mount the shared folder as /opt/shared with the docker container.  This will allow apps created within the docker container to persist outside of it.  This also means you can edit those files from outside the container--for example, when you're writing tests, etc.
For even more helpfulness, try setting your npm test command to run embark test.