0.19: Mention pcwalton's rendering perf optimization work

Screenshots for 0.19 release notes

Harper Integration

Reopen pagefind PR and fix deploy

Consider hosting an official forum under the Bevy domain instead of relying mainly on GitHub Discussions

Allow content to be submitted to the assets section directly from the website

Make the homepage more visually engaging

Tracking issue: Make the Bevy website more dynamic and engaging

Add example and short section about schedule in the introduction chapter of the book

Link the Figma Document/Design language/Design standards in more places in the contributor guide.