changed contribute docs link to writing docs

Author: story645

doc/devel/index.rst

@@ -45,7 +45,7 @@ process or how to fix something feel free to ask on `gitter
 
 .. rst-class:: sd-d-inline-block
 
-    .. button-ref:: contributing_documentation
+    .. button-ref:: documenting-matplotlib
         :class: sd-fs-6
         :color: primary