Mention cliff.sphinxext in Sphinx integration docs

I see that this is already fixed in the latest version of the docs:
https://docs.openstack.org/cliff/latest/user/sphinxext.html#preparation

I had found https://docs.openstack.org/cliff/2.6.0/sphinxext.html with Google and didn't notice that I'm looking at an old version of the docs.

Would it be possible for you to add some info to your docs system what versions are available and to go to the latest dev or stable version of the docs?

Having dates for the releases in the change log would also be nice.
See https://docs.openstack.org/cliff/latest/user/history.html

Finally, here you currently say Github, but the URLs are not pointing to Github:
https://docs.openstack.org/cliff/latest/install/index.html#reporting-bugs
```
Source Code
The source is hosted on github: https://git.openstack.org/cgit/openstack/cliff

Reporting Bugs
Please report bugs through the github project: https://bugs.launchpad.net/python-cliff
```
Can you please clarify this repo / tracker info in the docs? I guess the URLs are correct and just the text should not say "github"?

Thanks for reporting these doc issues.

We're working on a way to link from old versions to new ones.

Please do use launchpad for bugs and the primary git repo is http://git.openstack.org/cgit/openstack/cliff. I will update those docs shortly.