Updating cloud setup and local installation sections

[Alim-faraji]

Both sections are outdated as @wupeifan mentioned.
"1.This is a set of issues that we should change in cloud setup and local installation when switching from the old site to the new one:
1a. We should probably rewrite part of the cloud setup part. The previous "hover your mouse... and select..." doesn't work any more. And we should probably add some description for private hubs. Moreover, the description for binder hub is a bit terse.
1b. I thought there was an issue somewhere to update the screenshots in "local installation", but it seems that it was using the old ones. While I think it doesn't really matter very much, the updates are still pending. Also, the way to download the notebook changed since we now have a different UI, so we should probably rewrite part of it.
1c. Similarly, the "troubleshooting" part seems to be now completely different. Need some updates too."

[wupeifan]

We'll keep this open until a bunch of new qe-theme is updated.

[wupeifan]

We still need to revisit this after the new qe-theme is updated. The edits done in #144 is good enough for now, but we need to keep this issue open as a reminder.