Merge pull request #379 from cpoerschke/pr-7

add 'building cython code' in doc/contributing.rst

doc/contributing.rst

@@ -134,7 +134,15 @@ of the documentation, run::
 
   xdg-open _build/html/index.html
 
+Building Cython code
+--------------------
+
+Part of the code base is written in `Cython`_. To rebuild this code after making changes, please re-run the install command from the 'Setting up a Development Environment' section.
+
+If you are new to Cython you may find the project's documentation on `debugging <https://cython.readthedocs.io/en/latest/src/userguide/debugging.html>`_ and `profiling <https://cython.readthedocs.io/en/latest/src/tutorial/profiling_tutorial.html>`_ helpful.
+
 .. _conda: https://conda.io/miniconda.html
+.. _Cython: https://cython.org
 .. _Git: https://git-scm.com/
 .. _GitHub: https://github.com/sebp/scikit-survival
 .. _Sphinx: https://www.sphinx-doc.org/