Ensure current docs all have valid links

[qreeves]

During the initial port of the wiki to the docs, many pages were created with links to items that don't exist. Before release, we need to tie up these endpoints either with a valid page or removing the link so users don't get misled.

[nochinator]

many of the broken links have been fixed in #13 however there are still some broken links

[qreeves]

Main documentation landing page has many broken links now.

[Kissaki]

The Home page has an invalid link **[Editing Reference](editing/Reference.md)** - A detailed explanation of the available editor features.

Seeing a migration from wiki mentioned here, looking into a web archive, I can see that the wiki main page had an external link labeled Cube2 - Editing Reference (specifics may differ).

Is the current link supposed to be a replacement for that? A placeholder? An accidental replace?

Should it still link to sauerbraten? Can we drop it from the main page seeing as no content exists?

[Kissaki]

Jekyll seems to mark invalid links with <del>. This ticket is about those, right? We see them as striked-through on the website.

With a Jekyll setup in place (or a build artifact available) it should be a simple matter of searching for <del> to find the links in question.