Start a HACKING.md file and document how to run the tests

HACKING.md

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+# Hacking on Lorax
+
+Here's where to get the code:
+
+    $ git clone https://github.com/weldr/lorax
+    $ cd lorax/
+
+How to build it:
+
+    $ make
+
+## How to run the tests
+
+To run the tests you need the following dependencies installed:
+
+    $ yum install python3-nose python3-pytest-mock python3-pocketlint \
+		python3-mock
+
+Run the basic linting tests like this:
+
+    $ make check
+
+
+To run the broader unit and integration tests we use:
+
+    $ make test
+
+Some of the tests will be skipped unless a lorax-composer process is running
+and listening on an accessible socket. Either run lorax-composer from the
+checkout, or the installed version.
+