404.pug -> error404.pug.

web/templates/error404.pug

@@ -1,5 +1,8 @@
 extends base.pug
 
+block meta_description
+    meta(name='description' content='Not Found')
+
 block append head
     style(type="text/css").
         #error {
@@ -19,6 +22,7 @@ block nav
     h1 Oh, you lost? Bad for ya.
 
 block content
+    :go:func NotFound(title string)
     section#error
         h1 404
         | Page Not Found