Added references to the XML Interface Definitions and Unit Standards …

…documents to System-Architecture/CSC-Overview/index.rst.

System-Architecture/CSC-Overview/index.rst

@@ -181,6 +181,10 @@ These event topics are received by the listener, which can then be handled for f
 Telemetry is the on-going data stream generated by the CSC.
 It is published at a set rate.
 
+The full process for defining CSCs and all the topics is described in the `ts_xml README <https://github.com/lsst-ts/ts_xml/blob/main/README.md>`_.
+However, of particular interest is the policy regarding defining units in the XML definition files.
+For that, please refer to `XML Unit Standards :ref:`_XML_Units` document.
+
 Sources
 =======
 * `CSC Development <https://confluence.lsstcorp.org/pages/viewpage.action?spaceKey=LTS&title=CSC+Development>`_