DOC: updated build and test instructions.

doc/getting_started.rst

@@ -14,6 +14,18 @@ Prerequisites
 
 Only OpenCL!
 
+However: If you are a developer and are check out a version from GitHub. You will require `Cython <http://cython.org>`_. 
+
+If this is the case, when you run `python setup.py ...` you will see an error message like::
+
+    setup.py:66: UserWarning: Cython not installed using pre-cythonized files
+      warn("Cython not installed using pre-cythonized files", UserWarning, stacklevel=1)
+    Traceback (most recent call last):
+      File "setup.py", line 70, in <module>
+        raise Exception("Cython is required to build a c extension from a PYX file (solution get cython or checkout a release branch)")
+    Exception: Cython is required to build a c extension from a PYX file (solution get cython or checkout a release branch)
+
+
 Download
 --------------------
 
@@ -31,6 +43,17 @@ run::
 Test
 --------
 
-run::
+If you want to test an installed version
+you can run run::
 
+    python -c "import opencl; opencl.test()"
+
+.. warning:: Make sure you are not in the source directory.
+
+Otherwise to run tests from the source directory you must run::
+    
+    python setup.py build_ext --inplace
     python -m unittest discover opencl/
+
+.. note:: you can run these commands before you install as well
+