Show notification of new docs: web_extensions

assets/javascripts/news.json

@@ -1,7 +1,11 @@
 [
   [
-      "2021-05-26",
-      "New documentations: <a href=\"/latex/\">LaTeX</a>, <a href=\"/jq/\">jq</a>"
+    "2021-05-31",
+    "New documentation: <a href=\"/web_extensions/\">Web Extensions</a>"
+  ],
+  [
+    "2021-05-26",
+    "New documentations: <a href=\"/latex/\">LaTeX</a>, <a href=\"/jq/\">jq</a>"
   ],
   [
     "2021-04-29",