Point to external contributing guide.

Author: domdfcoding

doc-source/_templates/sidebar/navigation.html

@@ -138,9 +138,15 @@ Contents
 
 	usage
 	hooks
-	contributing
 	Source
 
+.. sidebar-links::
+	:caption: Links
+	:github:
+	:pypi: tox-recreate-hook
+
+	Contributing Guide <https://contributing-to-coincidence.readthedocs.io/en/latest/>
+
 .. start links
 
 .. only:: html

doc-source/contributing.rst

@@ -10,7 +10,7 @@ sphinx-notfound-page>=0.5
 sphinx-prompt>=1.1.0
 sphinx-pyproject>=0.1.0
 sphinx-tabs>=1.1.13
-sphinx-toolbox>=2.9.0
+sphinx-toolbox>=2.10.0
 sphinxcontrib-httpdomain>=1.7.0
 sphinxemoji>=0.1.6
 toctree-plus>=0.1.0