add link to stage 2.7 proposals table

Author: michaelficarra

_layouts/page_footer.html

@@ -144,6 +144,13 @@ <h3 id="proposals-label">{{ site["footer"]["proposals"] }}</h3>
               >Stage 2</a
             >
           </li>
+          
+          <li>
+            <a
+              href="https://github.com/tc39/proposals/blob/HEAD/README.md#stage-27"
+              >Stage 2.7</a
+            >
+          </li>
           <li>
             <a
               href="https://github.com/tc39/proposals/blob/HEAD/README.md#stage-3"