Improve troubleshooting section for restart

• 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)

Original created by @sajolida on 10632 (Redmine)