improve sitemap, fix typo in makrdown.md

Fixed vimrc typo relating to noexpandtab in `markdown.md`.

Added missing top level and 2nd level markdown and HTML files
to the sitemap.

Changed `bin/gen-sitemap.sh` VERSION from "2.0.0 2025-03-13"
to "2.0.1 2025-04-28".

Updated sitemap.

Tested the above via `make www gen_status gen_sitemap timestamp` on macOS.

markdown.html

@@ -614,7 +614,7 @@ following settings to make sure the tabs are not put in without you noticing:</p
 <pre><code>    set tabstop=8               &quot; a tab is 8 spaces (or whatever you wish it to be set to)
     set softtabstop=4           &quot; ...but when inserting/backspacing use 4 spaces
     set shiftwidth=4            &quot; ...and auto-indent 4 spaces (when autoindent is set)
-    set expandtab               &quot; ...but don&#39;t expand tab to spaces.</code></pre>
+    set noexpandtab             &quot; ...but don&#39;t expand tab to spaces.</code></pre>
 <p>If you have file type detection enabled you can, if you prefer, have these
 settings set just for markdown files:</p>
 <pre><code>    autocmd! Filetype markdown setlocal set tabstop=8 softtabstop=4 shiftwidth=4 expandtab</code></pre>