installation: unclear + bugs

CML "installation" is somewhat confusing, esp. to first-time users, I believe.

1. First, the Install element of the top website menu has some issues:

- It opens on hover but closes on click. Should at least have a little triangle (like Other Tools) to make it more intuitive because I immediately want to click on it (like Docs or Blog), which just closes it -- this may happen so fast you don't even see it ever open (bad UX).
- Once open (on hover) there's a gap so if you move the mouse too slow toward it, it actually closes again.
- The "as a package" distinction is probably lost completely for most people. I think it implies that you don't usually want to install CML directly right?
- Should it even be there if it's not a common need?

2. Then once you get to https://cml.dev/doc there's no clear indication of where/how CML gets installed. It's indirectly mentioned in a few places that it's included in the Docker images provided but I think we should be more explicit about this in intro docs like the https://cml.dev/doc/start index page and/or https://cml.dev/doc/usage

3. https://cml.dev/doc/install : is it linked from anywhere other than the top menu? I.e. why would I want to install CML as a a package?