docs: Add banner message about Devstack being deprecated

[sarina]

Addresses openedx/axim-engineering#1173

[sarina]

@robrap - I don't think docs run on devstack builds, but does this banner wording work for you?

[robrap]

@robrap - I don't think docs run on devstack builds,

What does this mean? That you don’t think you’ll get the banner? Other?

but does this banner wording work for you?

Thank you. This should imply what people need to do, but if you are open to it, you could add a really exploit note:

For any fork of devstack, you need to look elsewhere for up-to-date docs.

I’m ok if you think this is overkill, but otherwise, it just makes the seemingly obvious very explicit.

[sarina]

I like the additional wording, thanks.

I was looking through the CI tests, and I don't see an automated CI test for docs. I am in a low bandwidth environment and can't do a clone of this repo, so I can't build the docs myself.

[robrap]

I see. You just mean you can’t test locally? Are you willing to merge and see what happens?

[sarina]

I am so willing! haha