Consider merging the "demos", "WPT Pass Rates" and "Governance" pages into the website

[nicoburns]

Currently the following links in the servo navigation chuck you out of the servo website to a separate site:

• WPT Pass Rates (Include WPT scores directly in website #216)
• Demos (Inline servo demos into the website #224)
• Servo Starters (https://github.com/servo/servo-starters)
• Governance (https://github.com/servo/project/blob/main/governance/README.md)
• Servo Book (https://book.servo.org/)

The book I think would be a little tricky to integrate with the website, but the other 3 pages seem like they ought to just be a part of the main website rather than their own separate thing.

This would allow us to keep the same Servo branding across all of these locations. And would also allow users to easily navigate back from these pages to other parts of the servo website.

[nicoburns]

Servo Starters (https://github.com/servo/servo-starters) would also be a good candidate for this.