Add Docker Instructions (#122)

* Add Docker Instructions
* Add time

docs/source/Getting-Started/Running-Keystone-with-QEMU.rst

@@ -8,6 +8,38 @@ Keystone was tested in a QEMU fork in RISC-V (`GitHub <https://github.com/riscv/
 The upstream QEMU is not currently supported due to several remaining issues (Ex: `See GitHub issue <https://github.com/keystone-enclave/keystone/issues/25>`_).
 Fixes will be upstreamed in the future.
 
+If you just want to quickly test Keystone with QEMU, you can start with Docker, which will take <10
+minutes.
+Setting the environment by yourself (without Docker) will take 1-2 hours. 
+
+Start With Docker
+-----------------------
+The fastest way to try Keystone is through our `Docker <https://www.docker.com/>`_ image (Ubuntu 16.04/18.04).
+The image contains all of our source code, 
+as well as a compiled kernel, QEMU, example binaries, SDK, and GNU tools.
+Note that the source code in the Docker image may contain the latest release, not the latest branch.
+Always make sure you are working with the right version that matches with the documentation.
+
+Prerequisite: Docker
+
+Download the image and run a container.
+::
+
+  wget https://keystone-enclave.eecs.berkeley.edu/files/keystone-sample-image_docker.tgz
+  docker load --input keystone-sample-image_docker.tgz
+  docker run --name keystone-sample -it keystone-sample-image
+
+Now, run tests in the container. See :doc:`./QEMU-Run-Tests` for details.
+::
+  
+  # In the container
+  su keystone
+  cd ~/keystone
+  make run-tests 
+
+Start Without Docker
+-----------------------
+
 .. toctree::
    :maxdepth: 1