Adds how to run tests

Author: benbierens

docs/CodexHowTo.md

@@ -0,0 +1,9 @@
+# Codex Tests - How To
+Follow these steps to run the distributed tests for Codex. These tests should pass for any (future) release of Codex.
+
+## Build a docker image.
+If you already have a dist-tests compatible docker image, skip this step.
+![BuildImage](./CodexHowTo_BuildImage.png)
+
+## Run tests.
+![RunTests](./CodexHowTo_RunReleaseTests.png)