docs: Update contributing.rst

sp-files/contributing.rst

@@ -263,6 +263,10 @@ It is based on the `Canonical starter pack
 <https://canonical-starter-pack.readthedocs-hosted.com/latest/>`_
 and hosted on `Read the Docs <https://about.readthedocs.com/>`_.
 
+For syntax help and guidelines,
+refer to the `Canonical style guides
+<https://canonical-documentation-with-sphinx-and-readthedocscom.readthedocs-hosted.com/#style-guides>`_.
+
 In structuring,
 the documentation employs the `Diátaxis <https://diataxis.fr/>`_ approach.