add note on retiring docs

Author: LiamConnors

_includes/layouts/docs_retirement_plug.html

@@ -0,0 +1,4 @@
+<div class="dash-plug">
+  <p><strong>Note:</strong> We are retiring documentation for R, MATLAB, Julia, and F# in November 2025. <a href="https://community.plotly.com/t/retire-the-documentation-for-r-matlab-julia-and-f/94147">Learn more about this change here.</a>
+  </p>
+</div>

_layouts/base.html

@@ -48,6 +48,9 @@ <h1>
                 {% endunless %}
                 {% include layouts/page-another-language.html %}
                 {% include layouts/dashplug.html %}
+                {% if page.language == "r" or page.language == "julia" or page.language == "fsharp" or page.permalink contains "matlab/" or page.permalink contains "ggplot2/" %}
+                {% include layouts/docs_retirement_plug.html %}
+                {% endif %}
               </div>
             </div>
           </div>