Using Sphinx warning and note paragraph directives.

README.rst

@@ -82,7 +82,11 @@ Compile Cython extensions
 Once you have installed the aforementioned tools follow these steps to build the Cython extension modules for gprMax:
 
 #. Open a Terminal (Linux/Mac OS X) or Command Prompt (Windows) and navigate into the gprMax directory.
-#. Compile the Cython extension modules using: :code:`python setup.py build_ext --inplace`. You should see a set of :code:`.c` source files and a set of :code:`.so` (Linux/Mac OS X) or :code:`.pyd` (Windows) compiled module files inside the gprMax directory. If you want to remove/clean Cython generated files, use :code:`python setup.py cleanall`.
+#. Compile the Cython extension modules using: :code:`python setup.py build_ext --inplace`. You should see a set of :code:`.c` source files and a set of :code:`.so` (Linux/Mac OS X) or :code:`.pyd` (Windows) compiled module files inside the gprMax directory.
+
+.. note::
+
+    If you want to remove/clean Cython generated files, e.g. before rebuilding the Cython extensions, yu can use :code:`python setup.py cleanall`.
 
 You are now ready to run gprMax.