Refactor README.md and docs

[upbqdn]

Motivation

Prepare for releasing v1.8.

Solution

• Move "Known Issues" from README to the book
• Remove an old note from the book
• Move optional configs & features to the book
• Refactor the section on installing Zebra
• Fix badges in README.md

Tests

Not needed since this is only a docs refactor.

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.

[arya2]

This looks good, thank you!