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.md

@@ -321,7 +321,7 @@ following settings to make sure the tabs are not put in without you noticing:
     set tabstop=8		" a tab is 8 spaces (or whatever you wish it to be set to)
     set softtabstop=4		" ...but when inserting/backspacing use 4 spaces
     set shiftwidth=4		" ...and auto-indent 4 spaces (when autoindent is set)
-    set expandtab		" ...but don't expand tab to spaces.
+    set noexpandtab		" ...but don't expand tab to spaces.
 ```
 
 If you have file type detection enabled you can, if you prefer, have these