[Docs] Combine non-migrated content into single project

[jf205]

Partially fixes https://github.com/github/semmle-docs/issues/277.

[felicitymay]

The changes all make sense. The only thing that I wanted to highlight was that this doesn't entirely fix https://github.com/github/semmle-docs/issues/277.

If we're going to close that issue with this PR, then we need to put the information from two comments somewhere we'll remember them:

• .htaccess notes
• Explanatory banners

The first is obviously important and perhaps needs to go into the launch issue, or as a nested task on that issue? The second seems like a very good idea but could be a follow up issue.

[jf205]

The changes all make sense. The only thing that I wanted to highlight was that this doesn't entirely fix github/semmle-docs#277.

If we're going to close that issue with this PR, then we need to put the information from two comments somewhere we'll remember them:

• .htaccess notes
• Explanatory banners

The first is obviously important and perhaps needs to go into the launch issue, or as a nested task on that issue? The second seems like a very good idea but could be a follow up issue.

Thanks @felicitymay. You're quite right about the redirects and banners. I've created issues for those tasks 👍🏻