Add toc to remove sites document

[jcs090218]

This patch add table of content on the top for document removed_sites.md.

Notice this isn't a necessary patch yet I think this enhance the document by having the functionality to search for the target website.

[jayzeng]

A better idea will be use GitHub Actions to autogen toc and maintain sites.md

[jcs090218]

@jayzeng True, any idea on this?