Rewrite /doc/about/trust (#18025)

Closes #18025 (closed)

• Shorten by 35%
• Explain reproducible builds
• Reuse testimonials
• Don't pretend that users can understand our source code
• Don't pretend that Debian and Tor are looking closely at our work
• Mention the NSA :)
• Mention easy-to-use download verification
• Don't link to empty list of audits
• Make the different arguments scannable