Improve troubleshooting section for restart

Originally created by @sajolida on #10632 (Redmine)

• Move shutdown before boot menu key [77] [79]
• Explain to press-and-hold boot menu key before powering on [77]
• Link to website of computer vendors in list of boot menu keys
• Mention faulty USB sticks

Feature Branch: web/10632-restart-troubleshooting

Parent Task: #8592 (closed)

Related issues

• Related to #10649 (closed)